Google Git
Sign in
android / platform / libcore / c3a9db8 / . / ojluni / src / main / java / java / util / Collections.java
blob: 7194899bcdae57d3f583a6e59c85447654f7fe87 [file] [log] [blame]
/*
* Copyright (C) 2014 The Android Open Source Project
* Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.function.BiConsumer;
import java.util.function.Consumer;
/**
* This class consists exclusively of static methods that operate on or return
* collections. It contains polymorphic algorithms that operate on
* collections, "wrappers", which return a new collection backed by a
* specified collection, and a few other odds and ends.
*
* <p>The methods of this class all throw a <tt>NullPointerException</tt>
* if the collections or class objects provided to them are null.
*
* <p>The documentation for the polymorphic algorithms contained in this class
* generally includes a brief description of the <i>implementation</i>. Such
* descriptions should be regarded as <i>implementation notes</i>, rather than
* parts of the <i>specification</i>. Implementors should feel free to
* substitute other algorithms, so long as the specification itself is adhered
* to. (For example, the algorithm used by <tt>sort</tt> does not have to be
* a mergesort, but it does have to be <i>stable</i>.)
*
* <p>The "destructive" algorithms contained in this class, that is, the
* algorithms that modify the collection on which they operate, are specified
* to throw <tt>UnsupportedOperationException</tt> if the collection does not
* support the appropriate mutation primitive(s), such as the <tt>set</tt>
* method. These algorithms may, but are not required to, throw this
* exception if an invocation would have no effect on the collection. For
* example, invoking the <tt>sort</tt> method on an unmodifiable list that is
* already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
*
* <p>This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @see Set
* @see List
* @see Map
* @since 1.2
*/
public class Collections {
// Suppresses default constructor, ensuring non-instantiability.
private Collections() {
}
// Algorithms
/*
* Tuning parameters for algorithms - Many of the List algorithms have
* two implementations, one of which is appropriate for RandomAccess
* lists, the other for "sequential." Often, the random access variant
* yields better performance on small sequential access lists. The
* tuning parameters below determine the cutoff point for what constitutes
* a "small" sequential access list for each algorithm. The values below
* were empirically determined to work well for LinkedList. Hopefully
* they should be reasonable for other sequential access List
* implementations. Those doing performance work on this code would
* do well to validate the values of these parameters from time to time.
* (The first word of each tuning parameter name is the algorithm to which
* it applies.)
*/
private static final int BINARYSEARCH_THRESHOLD = 5000;
private static final int REVERSE_THRESHOLD = 18;
private static final int SHUFFLE_THRESHOLD = 5;
private static final int FILL_THRESHOLD = 25;
private static final int ROTATE_THRESHOLD = 100;
private static final int COPY_THRESHOLD = 10;
private static final int REPLACEALL_THRESHOLD = 11;
private static final int INDEXOFSUBLIST_THRESHOLD = 35;
/**
* Sorts the specified list into ascending order, according to the
* {@linkplain Comparable natural ordering} of its elements.
* All elements in the list must implement the {@link Comparable}
* interface. Furthermore, all elements in the list must be
* <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}
* must not throw a {@code ClassCastException} for any elements
* {@code e1} and {@code e2} in the list).
*
* <p>This sort is guaranteed to be <i>stable</i>: equal elements will
* not be reordered as a result of the sort.
*
* <p>The specified list must be modifiable, but need not be resizable.
*
* <p>Implementation note: This implementation is a stable, adaptive,
* iterative mergesort that requires far fewer than n lg(n) comparisons
* when the input array is partially sorted, while offering the
* performance of a traditional mergesort when the input array is
* randomly ordered. If the input array is nearly sorted, the
* implementation requires approximately n comparisons. Temporary
* storage requirements vary from a small constant for nearly sorted
* input arrays to n/2 object references for randomly ordered input
* arrays.
*
* <p>The implementation takes equal advantage of ascending and
* descending order in its input array, and can take advantage of
* ascending and descending order in different parts of the same
* input array. It is well-suited to merging two or more sorted arrays:
* simply concatenate the arrays and sort the resulting array.
*
* <p>The implementation was adapted from Tim Peters's list sort for Python
* (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
* TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic
* Sorting and Information Theoretic Complexity", in Proceedings of the
* Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
* January 1993.
*
* <p>This implementation dumps the specified list into an array, sorts
* the array, and iterates over the list resetting each element
* from the corresponding position in the array. This avoids the
* n<sup>2</sup> log(n) performance that would result from attempting
* to sort a linked list in place.
*
* @param list the list to be sorted.
* @throws ClassCastException if the list contains elements that are not
* <i>mutually comparable</i> (for example, strings and integers).
* @throws UnsupportedOperationException if the specified list's
* list-iterator does not support the {@code set} operation.
* @throws IllegalArgumentException (optional) if the implementation
* detects that the natural ordering of the list elements is
* found to violate the {@link Comparable} contract
*/
public static <T extends Comparable<? super T>> void sort(List<T> list) {
if (list.getClass() == ArrayList.class) {
Arrays.sort(((ArrayList) list).elementData, 0, list.size());
return;
}
Object[] a = list.toArray();
Arrays.sort(a);
ListIterator<T> i = list.listIterator();
for (int j=0; j<a.length; j++) {
i.next();
i.set((T)a[j]);
}
}
/**
* Sorts the specified list according to the order induced by the
* specified comparator. All elements in the list must be <i>mutually
* comparable</i> using the specified comparator (that is,
* {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
* for any elements {@code e1} and {@code e2} in the list).
*
* <p>This sort is guaranteed to be <i>stable</i>: equal elements will
* not be reordered as a result of the sort.
*
* <p>The specified list must be modifiable, but need not be resizable.
*
* <p>Implementation note: This implementation is a stable, adaptive,
* iterative mergesort that requires far fewer than n lg(n) comparisons
* when the input array is partially sorted, while offering the
* performance of a traditional mergesort when the input array is
* randomly ordered. If the input array is nearly sorted, the
* implementation requires approximately n comparisons. Temporary
* storage requirements vary from a small constant for nearly sorted
* input arrays to n/2 object references for randomly ordered input
* arrays.
*
* <p>The implementation takes equal advantage of ascending and
* descending order in its input array, and can take advantage of
* ascending and descending order in different parts of the same
* input array. It is well-suited to merging two or more sorted arrays:
* simply concatenate the arrays and sort the resulting array.
*
* <p>The implementation was adapted from Tim Peters's list sort for Python
* (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
* TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic
* Sorting and Information Theoretic Complexity", in Proceedings of the
* Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
* January 1993.
*
* <p>This implementation dumps the specified list into an array, sorts
* the array, and iterates over the list resetting each element
* from the corresponding position in the array. This avoids the
* n<sup>2</sup> log(n) performance that would result from attempting
* to sort a linked list in place.
*
* @param list the list to be sorted.
* @param c the comparator to determine the order of the list. A
* {@code null} value indicates that the elements' <i>natural
* ordering</i> should be used.
* @throws ClassCastException if the list contains elements that are not
* <i>mutually comparable</i> using the specified comparator.
* @throws UnsupportedOperationException if the specified list's
* list-iterator does not support the {@code set} operation.
* @throws IllegalArgumentException (optional) if the comparator is
* found to violate the {@link Comparator} contract
*/
public static <T> void sort(List<T> list, Comparator<? super T> c) {
if (list.getClass() == ArrayList.class) {
Arrays.sort(((ArrayList) list).elementData, 0, list.size(), (Comparator) c);
return;
}
Object[] a = list.toArray();
Arrays.sort(a, (Comparator)c);
ListIterator i = list.listIterator();
for (int j=0; j<a.length; j++) {
i.next();
i.set(a[j]);
}
}
/**
* Searches the specified list for the specified object using the binary
* search algorithm. The list must be sorted into ascending order
* according to the {@linkplain Comparable natural ordering} of its
* elements (as by the {@link #sort(List)} method) prior to making this
* call. If it is not sorted, the results are undefined. If the list
* contains multiple elements equal to the specified object, there is no
* guarantee which one will be found.
*
* <p>This method runs in log(n) time for a "random access" list (which
* provides near-constant-time positional access). If the specified list
* does not implement the {@link RandomAccess} interface and is large,
* this method will do an iterator-based binary search that performs
* O(n) link traversals and O(log n) element comparisons.
*
* @param list the list to be searched.
* @param key the key to be searched for.
* @return the index of the search key, if it is contained in the list;
* otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
* <i>insertion point</i> is defined as the point at which the
* key would be inserted into the list: the index of the first
* element greater than the key, or <tt>list.size()</tt> if all
* elements in the list are less than the specified key. Note
* that this guarantees that the return value will be &gt;= 0 if
* and only if the key is found.
* @throws ClassCastException if the list contains elements that are not
* <i>mutually comparable</i> (for example, strings and
* integers), or the search key is not mutually comparable
* with the elements of the list.
*/
public static <T>
int binarySearch(List<? extends Comparable<? super T>> list, T key) {
if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
return Collections.indexedBinarySearch(list, key);
else
return Collections.iteratorBinarySearch(list, key);
}
private static <T>
int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
{
int low = 0;
int high = list.size()-1;
while (low <= high) {
int mid = (low + high) >>> 1;
Comparable<? super T> midVal = list.get(mid);
int cmp = midVal.compareTo(key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
private static <T>
int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
{
int low = 0;
int high = list.size()-1;
ListIterator<? extends Comparable<? super T>> i = list.listIterator();
while (low <= high) {
int mid = (low + high) >>> 1;
Comparable<? super T> midVal = get(i, mid);
int cmp = midVal.compareTo(key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
/**
* Gets the ith element from the given list by repositioning the specified
* list listIterator.
*/
private static <T> T get(ListIterator<? extends T> i, int index) {
T obj = null;
int pos = i.nextIndex();
if (pos <= index) {
do {
obj = i.next();
} while (pos++ < index);
} else {
do {
obj = i.previous();
} while (--pos > index);
}
return obj;
}
/**
* Searches the specified list for the specified object using the binary
* search algorithm. The list must be sorted into ascending order
* according to the specified comparator (as by the
* {@link #sort(List, Comparator) sort(List, Comparator)}
* method), prior to making this call. If it is
* not sorted, the results are undefined. If the list contains multiple
* elements equal to the specified object, there is no guarantee which one
* will be found.
*
* <p>This method runs in log(n) time for a "random access" list (which
* provides near-constant-time positional access). If the specified list
* does not implement the {@link RandomAccess} interface and is large,
* this method will do an iterator-based binary search that performs
* O(n) link traversals and O(log n) element comparisons.
*
* @param list the list to be searched.
* @param key the key to be searched for.
* @param c the comparator by which the list is ordered.
* A <tt>null</tt> value indicates that the elements'
* {@linkplain Comparable natural ordering} should be used.
* @return the index of the search key, if it is contained in the list;
* otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
* <i>insertion point</i> is defined as the point at which the
* key would be inserted into the list: the index of the first
* element greater than the key, or <tt>list.size()</tt> if all
* elements in the list are less than the specified key. Note
* that this guarantees that the return value will be &gt;= 0 if
* and only if the key is found.
* @throws ClassCastException if the list contains elements that are not
* <i>mutually comparable</i> using the specified comparator,
* or the search key is not mutually comparable with the
* elements of the list using this comparator.
*/
public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
if (c==null)
return binarySearch((List) list, key);
if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
return Collections.indexedBinarySearch(list, key, c);
else
return Collections.iteratorBinarySearch(list, key, c);
}
private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
int low = 0;
int high = l.size()-1;
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = l.get(mid);
int cmp = c.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
int low = 0;
int high = l.size()-1;
ListIterator<? extends T> i = l.listIterator();
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = get(i, mid);
int cmp = c.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
private interface SelfComparable extends Comparable<SelfComparable> {}
/**
* Reverses the order of the elements in the specified list.<p>
*
* This method runs in linear time.
*
* @param list the list whose elements are to be reversed.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> operation.
*/
public static void reverse(List<?> list) {
int size = list.size();
if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
swap(list, i, j);
} else {
ListIterator fwd = list.listIterator();
ListIterator rev = list.listIterator(size);
for (int i=0, mid=list.size()>>1; i<mid; i++) {
Object tmp = fwd.next();
fwd.set(rev.previous());
rev.set(tmp);
}
}
}
/**
* Randomly permutes the specified list using a default source of
* randomness. All permutations occur with approximately equal
* likelihood.<p>
*
* The hedge "approximately" is used in the foregoing description because
* default source of randomness is only approximately an unbiased source
* of independently chosen bits. If it were a perfect source of randomly
* chosen bits, then the algorithm would choose permutations with perfect
* uniformity.<p>
*
* This implementation traverses the list backwards, from the last element
* up to the second, repeatedly swapping a randomly selected element into
* the "current position". Elements are randomly selected from the
* portion of the list that runs from the first element to the current
* position, inclusive.<p>
*
* This method runs in linear time. If the specified list does not
* implement the {@link RandomAccess} interface and is large, this
* implementation dumps the specified list into an array before shuffling
* it, and dumps the shuffled array back into the list. This avoids the
* quadratic behavior that would result from shuffling a "sequential
* access" list in place.
*
* @param list the list to be shuffled.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> operation.
*/
public static void shuffle(List<?> list) {
Random rnd = r;
if (rnd == null)
r = rnd = new Random();
shuffle(list, rnd);
}
private static Random r;
/**
* Randomly permute the specified list using the specified source of
* randomness. All permutations occur with equal likelihood
* assuming that the source of randomness is fair.<p>
*
* This implementation traverses the list backwards, from the last element
* up to the second, repeatedly swapping a randomly selected element into
* the "current position". Elements are randomly selected from the
* portion of the list that runs from the first element to the current
* position, inclusive.<p>
*
* This method runs in linear time. If the specified list does not
* implement the {@link RandomAccess} interface and is large, this
* implementation dumps the specified list into an array before shuffling
* it, and dumps the shuffled array back into the list. This avoids the
* quadratic behavior that would result from shuffling a "sequential
* access" list in place.
*
* @param list the list to be shuffled.
* @param rnd the source of randomness to use to shuffle the list.
* @throws UnsupportedOperationException if the specified list or its
* list-iterator does not support the <tt>set</tt> operation.
*/
public static void shuffle(List<?> list, Random rnd) {
int size = list.size();
if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
for (int i=size; i>1; i--)
swap(list, i-1, rnd.nextInt(i));
} else {
Object arr[] = list.toArray();
// Shuffle array
for (int i=size; i>1; i--)
swap(arr, i-1, rnd.nextInt(i));
// Dump array back into list
ListIterator it = list.listIterator();
for (int i=0; i<arr.length; i++) {
it.next();
it.set(arr[i]);
}
}
}
/**
* Swaps the elements at the specified positions in the specified list.
* (If the specified positions are equal, invoking this method leaves
* the list unchanged.)
*
* @param list The list in which to swap elements.
* @param i the index of one element to be swapped.
* @param j the index of the other element to be swapped.
* @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
* is out of range (i &lt; 0 || i &gt;= list.size()
* || j &lt; 0 || j &gt;= list.size()).
* @since 1.4
*/
public static void swap(List<?> list, int i, int j) {
final List l = list;
l.set(i, l.set(j, l.get(i)));
}
/**
* Swaps the two specified elements in the specified array.
*/
private static void swap(Object[] arr, int i, int j) {
Object tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
/**
* Replaces all of the elements of the specified list with the specified
* element. <p>
*
* This method runs in linear time.
*
* @param list the list to be filled with the specified element.
* @param obj The element with which to fill the specified list.
* @throws UnsupportedOperationException if the specified list or its
* list-iterator does not support the <tt>set</tt> operation.
*/
public static <T> void fill(List<? super T> list, T obj) {
int size = list.size();
if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
for (int i=0; i<size; i++)
list.set(i, obj);
} else {
ListIterator<? super T> itr = list.listIterator();
for (int i=0; i<size; i++) {
itr.next();
itr.set(obj);
}
}
}
/**
* Copies all of the elements from one list into another. After the
* operation, the index of each copied element in the destination list
* will be identical to its index in the source list. The destination
* list must be at least as long as the source list. If it is longer, the
* remaining elements in the destination list are unaffected. <p>
*
* This method runs in linear time.
*
* @param dest The destination list.
* @param src The source list.
* @throws IndexOutOfBoundsException if the destination list is too small
* to contain the entire source List.
* @throws UnsupportedOperationException if the destination list's
* list-iterator does not support the <tt>set</tt> operation.
*/
public static <T> void copy(List<? super T> dest, List<? extends T> src) {
int srcSize = src.size();
if (srcSize > dest.size())
throw new IndexOutOfBoundsException("Source does not fit in dest");
if (srcSize < COPY_THRESHOLD ||
(src instanceof RandomAccess && dest instanceof RandomAccess)) {
for (int i=0; i<srcSize; i++)
dest.set(i, src.get(i));
} else {
ListIterator<? super T> di=dest.listIterator();
ListIterator<? extends T> si=src.listIterator();
for (int i=0; i<srcSize; i++) {
di.next();
di.set(si.next());
}
}
}
/**
* Returns the minimum element of the given collection, according to the
* <i>natural ordering</i> of its elements. All elements in the
* collection must implement the <tt>Comparable</tt> interface.
* Furthermore, all elements in the collection must be <i>mutually
* comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
* <tt>e2</tt> in the collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of the collection.
*
* @param coll the collection whose minimum element is to be determined.
* @return the minimum element of the given collection, according
* to the <i>natural ordering</i> of its elements.
* @throws ClassCastException if the collection contains elements that are
* not <i>mutually comparable</i> (for example, strings and
* integers).
* @throws NoSuchElementException if the collection is empty.
* @see Comparable
*/
public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (next.compareTo(candidate) < 0)
candidate = next;
}
return candidate;
}
/**
* Returns the minimum element of the given collection, according to the
* order induced by the specified comparator. All elements in the
* collection must be <i>mutually comparable</i> by the specified
* comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
* <tt>e2</tt> in the collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of the collection.
*
* @param coll the collection whose minimum element is to be determined.
* @param comp the comparator with which to determine the minimum element.
* A <tt>null</tt> value indicates that the elements' <i>natural
* ordering</i> should be used.
* @return the minimum element of the given collection, according
* to the specified comparator.
* @throws ClassCastException if the collection contains elements that are
* not <i>mutually comparable</i> using the specified comparator.
* @throws NoSuchElementException if the collection is empty.
* @see Comparable
*/
public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
if (comp==null)
return (T)min((Collection<SelfComparable>) (Collection) coll);
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (comp.compare(next, candidate) < 0)
candidate = next;
}
return candidate;
}
/**
* Returns the maximum element of the given collection, according to the
* <i>natural ordering</i> of its elements. All elements in the
* collection must implement the <tt>Comparable</tt> interface.
* Furthermore, all elements in the collection must be <i>mutually
* comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
* <tt>e2</tt> in the collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of the collection.
*
* @param coll the collection whose maximum element is to be determined.
* @return the maximum element of the given collection, according
* to the <i>natural ordering</i> of its elements.
* @throws ClassCastException if the collection contains elements that are
* not <i>mutually comparable</i> (for example, strings and
* integers).
* @throws NoSuchElementException if the collection is empty.
* @see Comparable
*/
public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (next.compareTo(candidate) > 0)
candidate = next;
}
return candidate;
}
/**
* Returns the maximum element of the given collection, according to the
* order induced by the specified comparator. All elements in the
* collection must be <i>mutually comparable</i> by the specified
* comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
* <tt>e2</tt> in the collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of the collection.
*
* @param coll the collection whose maximum element is to be determined.
* @param comp the comparator with which to determine the maximum element.
* A <tt>null</tt> value indicates that the elements' <i>natural
* ordering</i> should be used.
* @return the maximum element of the given collection, according
* to the specified comparator.
* @throws ClassCastException if the collection contains elements that are
* not <i>mutually comparable</i> using the specified comparator.
* @throws NoSuchElementException if the collection is empty.
* @see Comparable
*/
public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
if (comp==null)
return (T)max((Collection<SelfComparable>) (Collection) coll);
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (comp.compare(next, candidate) > 0)
candidate = next;
}
return candidate;
}
/**
* Rotates the elements in the specified list by the specified distance.
* After calling this method, the element at index <tt>i</tt> will be
* the element previously at index <tt>(i - distance)</tt> mod
* <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
* and <tt>list.size()-1</tt>, inclusive. (This method has no effect on
* the size of the list.)
*
* <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
* After invoking <tt>Collections.rotate(list, 1)</tt> (or
* <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
* <tt>[s, t, a, n, k]</tt>.
*
* <p>Note that this method can usefully be applied to sublists to
* move one or more elements within a list while preserving the
* order of the remaining elements. For example, the following idiom
* moves the element at index <tt>j</tt> forward to position
* <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
* <pre>
* Collections.rotate(list.subList(j, k+1), -1);
* </pre>
* To make this concrete, suppose <tt>list</tt> comprises
* <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt>
* (<tt>b</tt>) forward two positions, perform the following invocation:
* <pre>
* Collections.rotate(l.subList(1, 4), -1);
* </pre>
* The resulting list is <tt>[a, c, d, b, e]</tt>.
*
* <p>To move more than one element forward, increase the absolute value
* of the rotation distance. To move elements backward, use a positive
* shift distance.
*
* <p>If the specified list is small or implements the {@link
* RandomAccess} interface, this implementation exchanges the first
* element into the location it should go, and then repeatedly exchanges
* the displaced element into the location it should go until a displaced
* element is swapped into the first element. If necessary, the process
* is repeated on the second and successive elements, until the rotation
* is complete. If the specified list is large and doesn't implement the
* <tt>RandomAccess</tt> interface, this implementation breaks the
* list into two sublist views around index <tt>-distance mod size</tt>.
* Then the {@link #reverse(List)} method is invoked on each sublist view,
* and finally it is invoked on the entire list. For a more complete
* description of both algorithms, see Section 2.3 of Jon Bentley's
* <i>Programming Pearls</i> (Addison-Wesley, 1986).
*
* @param list the list to be rotated.
* @param distance the distance to rotate the list. There are no
* constraints on this value; it may be zero, negative, or
* greater than <tt>list.size()</tt>.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> operation.
* @since 1.4
*/
public static void rotate(List<?> list, int distance) {
if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
rotate1(list, distance);
else
rotate2(list, distance);
}
private static <T> void rotate1(List<T> list, int distance) {
int size = list.size();
if (size == 0)
return;
distance = distance % size;
if (distance < 0)
distance += size;
if (distance == 0)
return;
for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
T displaced = list.get(cycleStart);
int i = cycleStart;
do {
i += distance;
if (i >= size)
i -= size;
displaced = list.set(i, displaced);
nMoved ++;
} while (i != cycleStart);
}
}
private static void rotate2(List<?> list, int distance) {
int size = list.size();
if (size == 0)
return;
int mid = -distance % size;
if (mid < 0)
mid += size;
if (mid == 0)
return;
reverse(list.subList(0, mid));
reverse(list.subList(mid, size));
reverse(list);
}
/**
* Replaces all occurrences of one specified value in a list with another.
* More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
* in <tt>list</tt> such that
* <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
* (This method has no effect on the size of the list.)
*
* @param list the list in which replacement is to occur.
* @param oldVal the old value to be replaced.
* @param newVal the new value with which <tt>oldVal</tt> is to be
* replaced.
* @return <tt>true</tt> if <tt>list</tt> contained one or more elements
* <tt>e</tt> such that
* <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> operation.
* @since 1.4
*/
public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
boolean result = false;
int size = list.size();
if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
if (oldVal==null) {
for (int i=0; i<size; i++) {
if (list.get(i)==null) {
list.set(i, newVal);
result = true;
}
}
} else {
for (int i=0; i<size; i++) {
if (oldVal.equals(list.get(i))) {
list.set(i, newVal);
result = true;
}
}
}
} else {
ListIterator<T> itr=list.listIterator();
if (oldVal==null) {
for (int i=0; i<size; i++) {
if (itr.next()==null) {
itr.set(newVal);
result = true;
}
}
} else {
for (int i=0; i<size; i++) {
if (oldVal.equals(itr.next())) {
itr.set(newVal);
result = true;
}
}
}
}
return result;
}
/**
* Returns the starting position of the first occurrence of the specified
* target list within the specified source list, or -1 if there is no
* such occurrence. More formally, returns the lowest index <tt>i</tt>
* such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
* or -1 if there is no such index. (Returns -1 if
* <tt>target.size() > source.size()</tt>.)
*
* <p>This implementation uses the "brute force" technique of scanning
* over the source list, looking for a match with the target at each
* location in turn.
*
* @param source the list in which to search for the first occurrence
* of <tt>target</tt>.
* @param target the list to search for as a subList of <tt>source</tt>.
* @return the starting position of the first occurrence of the specified
* target list within the specified source list, or -1 if there
* is no such occurrence.
* @since 1.4
*/
public static int indexOfSubList(List<?> source, List<?> target) {
int sourceSize = source.size();
int targetSize = target.size();
int maxCandidate = sourceSize - targetSize;
if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
(source instanceof RandomAccess&&target instanceof RandomAccess)) {
nextCand:
for (int candidate = 0; candidate <= maxCandidate; candidate++) {
for (int i=0, j=candidate; i<targetSize; i++, j++)
if (!eq(target.get(i), source.get(j)))
continue nextCand; // Element mismatch, try next cand
return candidate; // All elements of candidate matched target
}
} else { // Iterator version of above algorithm
ListIterator<?> si = source.listIterator();
nextCand:
for (int candidate = 0; candidate <= maxCandidate; candidate++) {
ListIterator<?> ti = target.listIterator();
for (int i=0; i<targetSize; i++) {
if (!eq(ti.next(), si.next())) {
// Back up source iterator to next candidate
for (int j=0; j<i; j++)
si.previous();
continue nextCand;
}
}
return candidate;
}
}
return -1; // No candidate matched the target
}
/**
* Returns the starting position of the last occurrence of the specified
* target list within the specified source list, or -1 if there is no such
* occurrence. More formally, returns the highest index <tt>i</tt>
* such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
* or -1 if there is no such index. (Returns -1 if
* <tt>target.size() > source.size()</tt>.)
*
* <p>This implementation uses the "brute force" technique of iterating
* over the source list, looking for a match with the target at each
* location in turn.
*
* @param source the list in which to search for the last occurrence
* of <tt>target</tt>.
* @param target the list to search for as a subList of <tt>source</tt>.
* @return the starting position of the last occurrence of the specified
* target list within the specified source list, or -1 if there
* is no such occurrence.
* @since 1.4
*/
public static int lastIndexOfSubList(List<?> source, List<?> target) {
int sourceSize = source.size();
int targetSize = target.size();
int maxCandidate = sourceSize - targetSize;
if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
source instanceof RandomAccess) { // Index access version
nextCand:
for (int candidate = maxCandidate; candidate >= 0; candidate--) {
for (int i=0, j=candidate; i<targetSize; i++, j++)
if (!eq(target.get(i), source.get(j)))
continue nextCand; // Element mismatch, try next cand
return candidate; // All elements of candidate matched target
}
} else { // Iterator version of above algorithm
if (maxCandidate < 0)
return -1;
ListIterator<?> si = source.listIterator(maxCandidate);
nextCand:
for (int candidate = maxCandidate; candidate >= 0; candidate--) {
ListIterator<?> ti = target.listIterator();
for (int i=0; i<targetSize; i++) {
if (!eq(ti.next(), si.next())) {
if (candidate != 0) {
// Back up source iterator to next candidate
for (int j=0; j<=i+1; j++)
si.previous();
}
continue nextCand;
}
}
return candidate;
}
}
return -1; // No candidate matched the target
}
// Unmodifiable Wrappers
/**
* Returns an unmodifiable view of the specified collection. This method
* allows modules to provide users with "read-only" access to internal
* collections. Query operations on the returned collection "read through"
* to the specified collection, and attempts to modify the returned
* collection, whether direct or via its iterator, result in an
* <tt>UnsupportedOperationException</tt>.<p>
*
* The returned collection does <i>not</i> pass the hashCode and equals
* operations through to the backing collection, but relies on
* <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This
* is necessary to preserve the contracts of these operations in the case
* that the backing collection is a set or a list.<p>
*
* The returned collection will be serializable if the specified collection
* is serializable.
*
* @param c the collection for which an unmodifiable view is to be
* returned.
* @return an unmodifiable view of the specified collection.
*/
public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
return new UnmodifiableCollection<>(c);
}
/**
* @serial include
*/
static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
private static final long serialVersionUID = 1820017752578914078L;
final Collection<? extends E> c;
UnmodifiableCollection(Collection<? extends E> c) {
if (c==null)
throw new NullPointerException();
this.c = c;
}
public int size() {return c.size();}
public boolean isEmpty() {return c.isEmpty();}
public boolean contains(Object o) {return c.contains(o);}
public Object[] toArray() {return c.toArray();}
public <T> T[] toArray(T[] a) {return c.toArray(a);}
public String toString() {return c.toString();}
public Iterator<E> iterator() {
return new Iterator<E>() {
private final Iterator<? extends E> i = c.iterator();
public boolean hasNext() {return i.hasNext();}
public E next() {return i.next();}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public boolean add(E e) {
throw new UnsupportedOperationException();
}
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
public boolean containsAll(Collection<?> coll) {
return c.containsAll(coll);
}
public boolean addAll(Collection<? extends E> coll) {
throw new UnsupportedOperationException();
}
public boolean removeAll(Collection<?> coll) {
throw new UnsupportedOperationException();
}
public boolean retainAll(Collection<?> coll) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
c.forEach(action);
}
}
/**
* Returns an unmodifiable view of the specified set. This method allows
* modules to provide users with "read-only" access to internal sets.
* Query operations on the returned set "read through" to the specified
* set, and attempts to modify the returned set, whether direct or via its
* iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
*
* The returned set will be serializable if the specified set
* is serializable.
*
* @param s the set for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified set.
*/
public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
return new UnmodifiableSet<>(s);
}
/**
* @serial include
*/
static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
implements Set<E>, Serializable {
private static final long serialVersionUID = -9215047833775013803L;
UnmodifiableSet(Set<? extends E> s) {super(s);}
public boolean equals(Object o) {return o == this || c.equals(o);}
public int hashCode() {return c.hashCode();}
}
/**
* Returns an unmodifiable view of the specified sorted set. This method
* allows modules to provide users with "read-only" access to internal
* sorted sets. Query operations on the returned sorted set "read
* through" to the specified sorted set. Attempts to modify the returned
* sorted set, whether direct, via its iterator, or via its
* <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
* an <tt>UnsupportedOperationException</tt>.<p>
*
* The returned sorted set will be serializable if the specified sorted set
* is serializable.
*
* @param s the sorted set for which an unmodifiable view is to be
* returned.
* @return an unmodifiable view of the specified sorted set.
*/
public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
return new UnmodifiableSortedSet<>(s);
}
/**
* @serial include
*/
static class UnmodifiableSortedSet<E>
extends UnmodifiableSet<E>
implements SortedSet<E>, Serializable {
private static final long serialVersionUID = -4929149591599911165L;
private final SortedSet<E> ss;
UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
public Comparator<? super E> comparator() {return ss.comparator();}
public SortedSet<E> subSet(E fromElement, E toElement) {
return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement));
}
public SortedSet<E> headSet(E toElement) {
return new UnmodifiableSortedSet<>(ss.headSet(toElement));
}
public SortedSet<E> tailSet(E fromElement) {
return new UnmodifiableSortedSet<>(ss.tailSet(fromElement));
}
public E first() {return ss.first();}
public E last() {return ss.last();}
}
/**
* Returns an unmodifiable view of the specified list. This method allows
* modules to provide users with "read-only" access to internal
* lists. Query operations on the returned list "read through" to the
* specified list, and attempts to modify the returned list, whether
* direct or via its iterator, result in an
* <tt>UnsupportedOperationException</tt>.<p>
*
* The returned list will be serializable if the specified list
* is serializable. Similarly, the returned list will implement
* {@link RandomAccess} if the specified list does.
*
* @param list the list for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified list.
*/
public static <T> List<T> unmodifiableList(List<? extends T> list) {
return (list instanceof RandomAccess ?
new UnmodifiableRandomAccessList<>(list) :
new UnmodifiableList<>(list));
}
/**
* @serial include
*/
static class UnmodifiableList<E> extends UnmodifiableCollection<E>
implements List<E> {
private static final long serialVersionUID = -283967356065247728L;
final List<? extends E> list;
UnmodifiableList(List<? extends E> list) {
super(list);
this.list = list;
}
public boolean equals(Object o) {return o == this || list.equals(o);}
public int hashCode() {return list.hashCode();}
public E get(int index) {return list.get(index);}
public E set(int index, E element) {
throw new UnsupportedOperationException();
}
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
public E remove(int index) {
throw new UnsupportedOperationException();
}
public int indexOf(Object o) {return list.indexOf(o);}
public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
public boolean addAll(int index, Collection<? extends E> c) {
throw new UnsupportedOperationException();
}
public ListIterator<E> listIterator() {return listIterator(0);}
public ListIterator<E> listIterator(final int index) {
return new ListIterator<E>() {
private final ListIterator<? extends E> i
= list.listIterator(index);
public boolean hasNext() {return i.hasNext();}
public E next() {return i.next();}
public boolean hasPrevious() {return i.hasPrevious();}
public E previous() {return i.previous();}
public int nextIndex() {return i.nextIndex();}
public int previousIndex() {return i.previousIndex();}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(E e) {
throw new UnsupportedOperationException();
}
public void add(E e) {
throw new UnsupportedOperationException();
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
}
/**
* UnmodifiableRandomAccessList instances are serialized as
* UnmodifiableList instances to allow them to be deserialized
* in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
* This method inverts the transformation. As a beneficial
* side-effect, it also grafts the RandomAccess marker onto
* UnmodifiableList instances that were serialized in pre-1.4 JREs.
*
* Note: Unfortunately, UnmodifiableRandomAccessList instances
* serialized in 1.4.1 and deserialized in 1.4 will become
* UnmodifiableList instances, as this method was missing in 1.4.
*/
private Object readResolve() {
return (list instanceof RandomAccess
? new UnmodifiableRandomAccessList<>(list)
: this);
}
}
/**
* @serial include
*/
static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
implements RandomAccess
{
UnmodifiableRandomAccessList(List<? extends E> list) {
super(list);
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableRandomAccessList<>(
list.subList(fromIndex, toIndex));
}
private static final long serialVersionUID = -2542308836966382001L;
/**
* Allows instances to be deserialized in pre-1.4 JREs (which do
* not have UnmodifiableRandomAccessList). UnmodifiableList has
* a readResolve method that inverts this transformation upon
* deserialization.
*/
private Object writeReplace() {
return new UnmodifiableList<>(list);
}
}
/**
* Returns an unmodifiable view of the specified map. This method
* allows modules to provide users with "read-only" access to internal
* maps. Query operations on the returned map "read through"
* to the specified map, and attempts to modify the returned
* map, whether direct or via its collection views, result in an
* <tt>UnsupportedOperationException</tt>.<p>
*
* The returned map will be serializable if the specified map
* is serializable.
*
* @param m the map for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified map.
*/
public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
return new UnmodifiableMap<>(m);
}
/**
* @serial include
*/
private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
private static final long serialVersionUID = -1034234728574286014L;
private final Map<? extends K, ? extends V> m;
UnmodifiableMap(Map<? extends K, ? extends V> m) {
if (m==null)
throw new NullPointerException();
this.m = m;
}
public int size() {return m.size();}
public boolean isEmpty() {return m.isEmpty();}
public boolean containsKey(Object key) {return m.containsKey(key);}
public boolean containsValue(Object val) {return m.containsValue(val);}
public V get(Object key) {return m.get(key);}
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
public V remove(Object key) {
throw new UnsupportedOperationException();
}
public void putAll(Map<? extends K, ? extends V> m) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;
public Set<K> keySet() {
if (keySet==null)
keySet = unmodifiableSet(m.keySet());
return keySet;
}
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = new UnmodifiableEntrySet<>(m.entrySet());
return entrySet;
}
public Collection<V> values() {
if (values==null)
values = unmodifiableCollection(m.values());
return values;
}
public boolean equals(Object o) {return o == this || m.equals(o);}
public int hashCode() {return m.hashCode();}
public String toString() {return m.toString();}
// Override default methods in Map
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
m.forEach(action);
}
/**
* We need this class in addition to UnmodifiableSet as
* Map.Entries themselves permit modification of the backing Map
* via their setValue operation. This class is subtle: there are
* many possible attacks that must be thwarted.
*
* @serial include
*/
static class UnmodifiableEntrySet<K,V>
extends UnmodifiableSet<Map.Entry<K,V>> {
private static final long serialVersionUID = 7854390611657943733L;
UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
super((Set)s);
}
static <K, V> Consumer<Map.Entry<K, V>> entryConsumer(Consumer<? super Entry<K, V>> action) {
return e -> action.accept(new UnmodifiableEntry<>(e));
}
// Override default methods in Collection
public void forEach(Consumer<? super Entry<K, V>> action) {
Objects.requireNonNull(action);
c.forEach(entryConsumer(action));
}
public Iterator<Map.Entry<K,V>> iterator() {
return new Iterator<Map.Entry<K,V>>() {
private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
public boolean hasNext() {
return i.hasNext();
}
public Map.Entry<K,V> next() {
return new UnmodifiableEntry<>(i.next());
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public Object[] toArray() {
Object[] a = c.toArray();
for (int i=0; i<a.length; i++)
a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]);
return a;
}
public <T> T[] toArray(T[] a) {
// We don't pass a to c.toArray, to avoid window of
// vulnerability wherein an unscrupulous multithreaded client
// could get his hands on raw (unwrapped) Entries from c.
Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
for (int i=0; i<arr.length; i++)
arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]);
if (arr.length > a.length)
return (T[])arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
/**
* This method is overridden to protect the backing set against
* an object with a nefarious equals function that senses
* that the equality-candidate is Map.Entry and calls its
* setValue method.
*/
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
return c.contains(
new UnmodifiableEntry<>((Map.Entry<?,?>) o));
}
/**
* The next two methods are overridden to protect against
* an unscrupulous List whose contains(Object o) method senses
* when o is a Map.Entry, and calls o.setValue.
*/
public boolean containsAll(Collection<?> coll) {
for (Object e : coll) {
if (!contains(e)) // Invokes safe contains() above
return false;
}
return true;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set s = (Set) o;
if (s.size() != c.size())
return false;
return containsAll(s); // Invokes safe containsAll() above
}
/**
* This "wrapper class" serves two purposes: it prevents
* the client from modifying the backing Map, by short-circuiting
* the setValue method, and it protects the backing Map against
* an ill-behaved Map.Entry that attempts to modify another
* Map Entry when asked to perform an equality check.
*/
private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
private Map.Entry<? extends K, ? extends V> e;
UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
public K getKey() {return e.getKey();}
public V getValue() {return e.getValue();}
public V setValue(V value) {
throw new UnsupportedOperationException();
}
public int hashCode() {return e.hashCode();}
public boolean equals(Object o) {
if (this == o)
return true;
if (!(o instanceof Map.Entry))
return false;
Map.Entry t = (Map.Entry)o;
return eq(e.getKey(), t.getKey()) &&
eq(e.getValue(), t.getValue());
}
public String toString() {return e.toString();}
}
}
}
/**
* Returns an unmodifiable view of the specified sorted map. This method
* allows modules to provide users with "read-only" access to internal
* sorted maps. Query operations on the returned sorted map "read through"
* to the specified sorted map. Attempts to modify the returned
* sorted map, whether direct, via its collection views, or via its
* <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
* an <tt>UnsupportedOperationException</tt>.<p>
*
* The returned sorted map will be serializable if the specified sorted map
* is serializable.
*
* @param m the sorted map for which an unmodifiable view is to be
* returned.
* @return an unmodifiable view of the specified sorted map.
*/
public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
return new UnmodifiableSortedMap<>(m);
}
/**
* @serial include
*/
static class UnmodifiableSortedMap<K,V>
extends UnmodifiableMap<K,V>
implements SortedMap<K,V>, Serializable {
private static final long serialVersionUID = -8806743815996713206L;
private final SortedMap<K, ? extends V> sm;
UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
public Comparator<? super K> comparator() {return sm.comparator();}
public SortedMap<K,V> subMap(K fromKey, K toKey) {
return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey));
}
public SortedMap<K,V> headMap(K toKey) {
return new UnmodifiableSortedMap<>(sm.headMap(toKey));
}
public SortedMap<K,V> tailMap(K fromKey) {
return new UnmodifiableSortedMap<>(sm.tailMap(fromKey));
}
public K firstKey() {return sm.firstKey();}
public K lastKey() {return sm.lastKey();}
}
// Synch Wrappers
/**
* Returns a synchronized (thread-safe) collection backed by the specified
* collection. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing collection is accomplished
* through the returned collection.<p>
*
* It is imperative that the user manually synchronize on the returned
* collection when iterating over it:
* <pre>
* Collection c = Collections.synchronizedCollection(myCollection);
* ...
* synchronized (c) {
* Iterator i = c.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
* and <tt>equals</tt> operations through to the backing collection, but
* relies on <tt>Object</tt>'s equals and hashCode methods. This is
* necessary to preserve the contracts of these operations in the case
* that the backing collection is a set or a list.<p>
*
* The returned collection will be serializable if the specified collection
* is serializable.
*
* @param c the collection to be "wrapped" in a synchronized collection.
* @return a synchronized view of the specified collection.
*/
public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
return new SynchronizedCollection<>(c);
}
static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
return new SynchronizedCollection<>(c, mutex);
}
/**
* @serial include
*/
static class SynchronizedCollection<E> implements Collection<E>, Serializable {
private static final long serialVersionUID = 3053995032091335093L;
final Collection<E> c; // Backing Collection
final Object mutex; // Object on which to synchronize
SynchronizedCollection(Collection<E> c) {
if (c==null)
throw new NullPointerException();
this.c = c;
mutex = this;
}
SynchronizedCollection(Collection<E> c, Object mutex) {
this.c = c;
this.mutex = mutex;
}
public int size() {
synchronized (mutex) {return c.size();}
}
public boolean isEmpty() {
synchronized (mutex) {return c.isEmpty();}
}
public boolean contains(Object o) {
synchronized (mutex) {return c.contains(o);}
}
public Object[] toArray() {
synchronized (mutex) {return c.toArray();}
}
public <T> T[] toArray(T[] a) {
synchronized (mutex) {return c.toArray(a);}
}
public Iterator<E> iterator() {
return c.iterator(); // Must be manually synched by user!
}
public boolean add(E e) {
synchronized (mutex) {return c.add(e);}
}
public boolean remove(Object o) {
synchronized (mutex) {return c.remove(o);}
}
public boolean containsAll(Collection<?> coll) {
synchronized (mutex) {return c.containsAll(coll);}
}
public boolean addAll(Collection<? extends E> coll) {
synchronized (mutex) {return c.addAll(coll);}
}
public boolean removeAll(Collection<?> coll) {
synchronized (mutex) {return c.removeAll(coll);}
}
public boolean retainAll(Collection<?> coll) {
synchronized (mutex) {return c.retainAll(coll);}
}
public void clear() {
synchronized (mutex) {c.clear();}
}
public String toString() {
synchronized (mutex) {return c.toString();}
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> consumer) {
synchronized (mutex) {c.forEach(consumer);}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized (mutex) {s.defaultWriteObject();}
}
}
/**
* Returns a synchronized (thread-safe) set backed by the specified
* set. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing set is accomplished
* through the returned set.<p>
*
* It is imperative that the user manually synchronize on the returned
* set when iterating over it:
* <pre>
* Set s = Collections.synchronizedSet(new HashSet());
* ...
* synchronized (s) {
* Iterator i = s.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned set will be serializable if the specified set is
* serializable.
*
* @param s the set to be "wrapped" in a synchronized set.
* @return a synchronized view of the specified set.
*/
public static <T> Set<T> synchronizedSet(Set<T> s) {
return new SynchronizedSet<>(s);
}
static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
return new SynchronizedSet<>(s, mutex);
}
/**
* @serial include
*/
static class SynchronizedSet<E>
extends SynchronizedCollection<E>
implements Set<E> {
private static final long serialVersionUID = 487447009682186044L;
SynchronizedSet(Set<E> s) {
super(s);
}
SynchronizedSet(Set<E> s, Object mutex) {
super(s, mutex);
}
public boolean equals(Object o) {
if (this == o)
return true;
synchronized (mutex) {return c.equals(o);}
}
public int hashCode() {
synchronized (mutex) {return c.hashCode();}
}
}
/**
* Returns a synchronized (thread-safe) sorted set backed by the specified
* sorted set. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing sorted set is accomplished
* through the returned sorted set (or its views).<p>
*
* It is imperative that the user manually synchronize on the returned
* sorted set when iterating over it or any of its <tt>subSet</tt>,
* <tt>headSet</tt>, or <tt>tailSet</tt> views.
* <pre>
* SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
* ...
* synchronized (s) {
* Iterator i = s.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* or:
* <pre>
* SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
* SortedSet s2 = s.headSet(foo);
* ...
* synchronized (s) { // Note: s, not s2!!!
* Iterator i = s2.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned sorted set will be serializable if the specified
* sorted set is serializable.
*
* @param s the sorted set to be "wrapped" in a synchronized sorted set.
* @return a synchronized view of the specified sorted set.
*/
public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
return new SynchronizedSortedSet<>(s);
}
/**
* @serial include
*/
static class SynchronizedSortedSet<E>
extends SynchronizedSet<E>
implements SortedSet<E>
{
private static final long serialVersionUID = 8695801310862127406L;
private final SortedSet<E> ss;
SynchronizedSortedSet(SortedSet<E> s) {
super(s);
ss = s;
}
SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
super(s, mutex);
ss = s;
}
public Comparator<? super E> comparator() {
synchronized (mutex) {return ss.comparator();}
}
public SortedSet<E> subSet(E fromElement, E toElement) {
synchronized (mutex) {
return new SynchronizedSortedSet<>(
ss.subSet(fromElement, toElement), mutex);
}
}
public SortedSet<E> headSet(E toElement) {
synchronized (mutex) {
return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
}
}
public SortedSet<E> tailSet(E fromElement) {
synchronized (mutex) {
return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex);
}
}
public E first() {
synchronized (mutex) {return ss.first();}
}
public E last() {
synchronized (mutex) {return ss.last();}
}
}
/**
* Returns a synchronized (thread-safe) list backed by the specified
* list. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing list is accomplished
* through the returned list.<p>
*
* It is imperative that the user manually synchronize on the returned
* list when iterating over it:
* <pre>
* List list = Collections.synchronizedList(new ArrayList());
* ...
* synchronized (list) {
* Iterator i = list.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned list will be serializable if the specified list is
* serializable.
*
* @param list the list to be "wrapped" in a synchronized list.
* @return a synchronized view of the specified list.
*/
public static <T> List<T> synchronizedList(List<T> list) {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList<>(list) :
new SynchronizedList<>(list));
}
static <T> List<T> synchronizedList(List<T> list, Object mutex) {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList<>(list, mutex) :
new SynchronizedList<>(list, mutex));
}
/**
* @serial include
*/
static class SynchronizedList<E>
extends SynchronizedCollection<E>
implements List<E> {
private static final long serialVersionUID = -7754090372962971524L;
final List<E> list;
SynchronizedList(List<E> list) {
super(list);
this.list = list;
}
SynchronizedList(List<E> list, Object mutex) {
super(list, mutex);
this.list = list;
}
public boolean equals(Object o) {
if (this == o)
return true;
synchronized (mutex) {return list.equals(o);}
}
public int hashCode() {
synchronized (mutex) {return list.hashCode();}
}
public E get(int index) {
synchronized (mutex) {return list.get(index);}
}
public E set(int index, E element) {
synchronized (mutex) {return list.set(index, element);}
}
public void add(int index, E element) {
synchronized (mutex) {list.add(index, element);}
}
public E remove(int index) {
synchronized (mutex) {return list.remove(index);}
}
public int indexOf(Object o) {
synchronized (mutex) {return list.indexOf(o);}
}
public int lastIndexOf(Object o) {
synchronized (mutex) {return list.lastIndexOf(o);}
}
public boolean addAll(int index, Collection<? extends E> c) {
synchronized (mutex) {return list.addAll(index, c);}
}
public ListIterator<E> listIterator() {
return list.listIterator(); // Must be manually synched by user
}
public ListIterator<E> listIterator(int index) {
return list.listIterator(index); // Must be manually synched by user
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized (mutex) {
return new SynchronizedList<>(list.subList(fromIndex, toIndex),
mutex);
}
}
/**
* SynchronizedRandomAccessList instances are serialized as
* SynchronizedList instances to allow them to be deserialized
* in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
* This method inverts the transformation. As a beneficial
* side-effect, it also grafts the RandomAccess marker onto
* SynchronizedList instances that were serialized in pre-1.4 JREs.
*
* Note: Unfortunately, SynchronizedRandomAccessList instances
* serialized in 1.4.1 and deserialized in 1.4 will become
* SynchronizedList instances, as this method was missing in 1.4.
*/
private Object readResolve() {
return (list instanceof RandomAccess
? new SynchronizedRandomAccessList<>(list)
: this);
}
}
/**
* @serial include
*/
static class SynchronizedRandomAccessList<E>
extends SynchronizedList<E>
implements RandomAccess {
SynchronizedRandomAccessList(List<E> list) {
super(list);
}
SynchronizedRandomAccessList(List<E> list, Object mutex) {
super(list, mutex);
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized (mutex) {
return new SynchronizedRandomAccessList<>(
list.subList(fromIndex, toIndex), mutex);
}
}
private static final long serialVersionUID = 1530674583602358482L;
/**
* Allows instances to be deserialized in pre-1.4 JREs (which do
* not have SynchronizedRandomAccessList). SynchronizedList has
* a readResolve method that inverts this transformation upon
* deserialization.
*/
private Object writeReplace() {
return new SynchronizedList<>(list);
}
}
/**
* Returns a synchronized (thread-safe) map backed by the specified
* map. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing map is accomplished
* through the returned map.<p>
*
* It is imperative that the user manually synchronize on the returned
* map when iterating over any of its collection views:
* <pre>
* Map m = Collections.synchronizedMap(new HashMap());
* ...
* Set s = m.keySet(); // Needn't be in synchronized block
* ...
* synchronized (m) { // Synchronizing on m, not s!
* Iterator i = s.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned map will be serializable if the specified map is
* serializable.
*
* @param m the map to be "wrapped" in a synchronized map.
* @return a synchronized view of the specified map.
*/
public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
return new SynchronizedMap<>(m);
}
/**
* @serial include
*/
private static class SynchronizedMap<K,V>
implements Map<K,V>, Serializable {
private static final long serialVersionUID = 1978198479659022715L;
private final Map<K,V> m; // Backing Map
final Object mutex; // Object on which to synchronize
SynchronizedMap(Map<K,V> m) {
if (m==null)
throw new NullPointerException();
this.m = m;
mutex = this;
}
SynchronizedMap(Map<K,V> m, Object mutex) {
this.m = m;
this.mutex = mutex;
}
public int size() {
synchronized (mutex) {return m.size();}
}
public boolean isEmpty() {
synchronized (mutex) {return m.isEmpty();}
}
public boolean containsKey(Object key) {
synchronized (mutex) {return m.containsKey(key);}
}
public boolean containsValue(Object value) {
synchronized (mutex) {return m.containsValue(value);}
}
public V get(Object key) {
synchronized (mutex) {return m.get(key);}
}
public V put(K key, V value) {
synchronized (mutex) {return m.put(key, value);}
}
public V remove(Object key) {
synchronized (mutex) {return m.remove(key);}
}
public void putAll(Map<? extends K, ? extends V> map) {
synchronized (mutex) {m.putAll(map);}
}
public void clear() {
synchronized (mutex) {m.clear();}
}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;
public Set<K> keySet() {
synchronized (mutex) {
if (keySet==null)
keySet = new SynchronizedSet<>(m.keySet(), mutex);
return keySet;
}
}
public Set<Map.Entry<K,V>> entrySet() {
synchronized (mutex) {
if (entrySet==null)
entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
return entrySet;
}
}
public Collection<V> values() {
synchronized (mutex) {
if (values==null)
values = new SynchronizedCollection<>(m.values(), mutex);
return values;
}
}
public boolean equals(Object o) {
if (this == o)
return true;
synchronized (mutex) {return m.equals(o);}
}
public int hashCode() {
synchronized (mutex) {return m.hashCode();}
}
public String toString() {
synchronized (mutex) {return m.toString();}
}
// Override default methods in Map
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
synchronized (mutex) {m.forEach(action);}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized (mutex) {s.defaultWriteObject();}
}
}
/**
* Returns a synchronized (thread-safe) sorted map backed by the specified
* sorted map. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing sorted map is accomplished
* through the returned sorted map (or its views).<p>
*
* It is imperative that the user manually synchronize on the returned
* sorted map when iterating over any of its collection views, or the
* collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
* <tt>tailMap</tt> views.
* <pre>
* SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
* ...
* Set s = m.keySet(); // Needn't be in synchronized block
* ...
* synchronized (m) { // Synchronizing on m, not s!
* Iterator i = s.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* or:
* <pre>
* SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
* SortedMap m2 = m.subMap(foo, bar);
* ...
* Set s2 = m2.keySet(); // Needn't be in synchronized block
* ...
* synchronized (m) { // Synchronizing on m, not m2 or s2!
* Iterator i = s.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned sorted map will be serializable if the specified
* sorted map is serializable.
*
* @param m the sorted map to be "wrapped" in a synchronized sorted map.
* @return a synchronized view of the specified sorted map.
*/
public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
return new SynchronizedSortedMap<>(m);
}
/**
* @serial include
*/
static class SynchronizedSortedMap<K,V>
extends SynchronizedMap<K,V>
implements SortedMap<K,V>
{
private static final long serialVersionUID = -8798146769416483793L;
private final SortedMap<K,V> sm;
SynchronizedSortedMap(SortedMap<K,V> m) {
super(m);
sm = m;
}
SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
super(m, mutex);
sm = m;
}
public Comparator<? super K> comparator() {
synchronized (mutex) {return sm.comparator();}
}
public SortedMap<K,V> subMap(K fromKey, K toKey) {
synchronized (mutex) {
return new SynchronizedSortedMap<>(
sm.subMap(fromKey, toKey), mutex);
}
}
public SortedMap<K,V> headMap(K toKey) {
synchronized (mutex) {
return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
}
}
public SortedMap<K,V> tailMap(K fromKey) {
synchronized (mutex) {
return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
}
}
public K firstKey() {
synchronized (mutex) {return sm.firstKey();}
}
public K lastKey() {
synchronized (mutex) {return sm.lastKey();}
}
}
// Dynamically typesafe collection wrappers
/**
* Returns a dynamically typesafe view of the specified collection.
* Any attempt to insert an element of the wrong type will result in an
* immediate {@link ClassCastException}. Assuming a collection
* contains no incorrectly typed elements prior to the time a
* dynamically typesafe view is generated, and that all subsequent
* access to the collection takes place through the view, it is
* <i>guaranteed</i> that the collection cannot contain an incorrectly
* typed element.
*
* <p>The generics mechanism in the language provides compile-time
* (static) type checking, but it is possible to defeat this mechanism
* with unchecked casts. Usually this is not a problem, as the compiler
* issues warnings on all such unchecked operations. There are, however,
* times when static type checking alone is not sufficient. For example,
* suppose a collection is passed to a third-party library and it is
* imperative that the library code not corrupt the collection by
* inserting an element of the wrong type.
*
* <p>Another use of dynamically typesafe views is debugging. Suppose a
* program fails with a {@code ClassCastException}, indicating that an
* incorrectly typed element was put into a parameterized collection.
* Unfortunately, the exception can occur at any time after the erroneous
* element is inserted, so it typically provides little or no information
* as to the real source of the problem. If the problem is reproducible,
* one can quickly determine its source by temporarily modifying the
* program to wrap the collection with a dynamically typesafe view.
* For example, this declaration:
* <pre> {@code
* Collection<String> c = new HashSet<String>();
* }</pre>
* may be replaced temporarily by this one:
* <pre> {@code
* Collection<String> c = Collections.checkedCollection(
* new HashSet<String>(), String.class);
* }</pre>
* Running the program again will cause it to fail at the point where
* an incorrectly typed element is inserted into the collection, clearly
* identifying the source of the problem. Once the problem is fixed, the
* modified declaration may be reverted back to the original.
*
* <p>The returned collection does <i>not</i> pass the hashCode and equals
* operations through to the backing collection, but relies on
* {@code Object}'s {@code equals} and {@code hashCode} methods. This
* is necessary to preserve the contracts of these operations in the case
* that the backing collection is a set or a list.
*
* <p>The returned collection will be serializable if the specified
* collection is serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned collection permits insertion of null elements
* whenever the backing collection does.
*
* @param c the collection for which a dynamically typesafe view is to be
* returned
* @param type the type of element that {@code c} is permitted to hold
* @return a dynamically typesafe view of the specified collection
* @since 1.5
*/
public static <E> Collection<E> checkedCollection(Collection<E> c,
Class<E> type) {
return new CheckedCollection<>(c, type);
}
@SuppressWarnings("unchecked")
static <T> T[] zeroLengthArray(Class<T> type) {
return (T[]) Array.newInstance(type, 0);
}
/**
* @serial include
*/
static class CheckedCollection<E> implements Collection<E>, Serializable {
private static final long serialVersionUID = 1578914078182001775L;
final Collection<E> c;
final Class<E> type;
void typeCheck(Object o) {
if (o != null && !type.isInstance(o))
throw new ClassCastException(badElementMsg(o));
}
private String badElementMsg(Object o) {
return "Attempt to insert " + o.getClass() +
" element into collection with element type " + type;
}
CheckedCollection(Collection<E> c, Class<E> type) {
if (c==null || type == null)
throw new NullPointerException();
this.c = c;
this.type = type;
}
public int size() { return c.size(); }
public boolean isEmpty() { return c.isEmpty(); }
public boolean contains(Object o) { return c.contains(o); }
public Object[] toArray() { return c.toArray(); }
public <T> T[] toArray(T[] a) { return c.toArray(a); }
public String toString() { return c.toString(); }
public boolean remove(Object o) { return c.remove(o); }
public void clear() { c.clear(); }
public boolean containsAll(Collection<?> coll) {
return c.containsAll(coll);
}
public boolean removeAll(Collection<?> coll) {
return c.removeAll(coll);
}
public boolean retainAll(Collection<?> coll) {
return c.retainAll(coll);
}
public Iterator<E> iterator() {
final Iterator<E> it = c.iterator();
return new Iterator<E>() {
public boolean hasNext() { return it.hasNext(); }
public E next() { return it.next(); }
public void remove() { it.remove(); }};
}
public boolean add(E e) {
typeCheck(e);
return c.add(e);
}
private E[] zeroLengthElementArray = null; // Lazily initialized
private E[] zeroLengthElementArray() {
return zeroLengthElementArray != null ? zeroLengthElementArray :
(zeroLengthElementArray = zeroLengthArray(type));
}
@SuppressWarnings("unchecked")
Collection<E> checkedCopyOf(Collection<? extends E> coll) {
Object[] a = null;
try {
E[] z = zeroLengthElementArray();
a = coll.toArray(z);
// Defend against coll violating the toArray contract
if (a.getClass() != z.getClass())
a = Arrays.copyOf(a, a.length, z.getClass());
} catch (ArrayStoreException ignore) {
// To get better and consistent diagnostics,
// we call typeCheck explicitly on each element.
// We call clone() to defend against coll retaining a
// reference to the returned array and storing a bad
// element into it after it has been type checked.
a = coll.toArray().clone();
for (Object o : a)
typeCheck(o);
}
// A slight abuse of the type system, but safe here.
return (Collection<E>) Arrays.asList(a);
}
public boolean addAll(Collection<? extends E> coll) {
// Doing things this way insulates us from concurrent changes
// in the contents of coll and provides all-or-nothing
// semantics (which we wouldn't get if we type-checked each
// element as we added it)
return c.addAll(checkedCopyOf(coll));
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {c.forEach(action);}
}
/**
* Returns a dynamically typesafe view of the specified set.
* Any attempt to insert an element of the wrong type will result in
* an immediate {@link ClassCastException}. Assuming a set contains
* no incorrectly typed elements prior to the time a dynamically typesafe
* view is generated, and that all subsequent access to the set
* takes place through the view, it is <i>guaranteed</i> that the
* set cannot contain an incorrectly typed element.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned set will be serializable if the specified set is
* serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned set permits insertion of null elements whenever
* the backing set does.
*
* @param s the set for which a dynamically typesafe view is to be
* returned
* @param type the type of element that {@code s} is permitted to hold
* @return a dynamically typesafe view of the specified set
* @since 1.5
*/
public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
return new CheckedSet<>(s, type);
}
/**
* @serial include
*/
static class CheckedSet<E> extends CheckedCollection<E>
implements Set<E>, Serializable
{
private static final long serialVersionUID = 4694047833775013803L;
CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
public boolean equals(Object o) { return o == this || c.equals(o); }
public int hashCode() { return c.hashCode(); }
}
/**
* Returns a dynamically typesafe view of the specified sorted set.
* Any attempt to insert an element of the wrong type will result in an
* immediate {@link ClassCastException}. Assuming a sorted set
* contains no incorrectly typed elements prior to the time a
* dynamically typesafe view is generated, and that all subsequent
* access to the sorted set takes place through the view, it is
* <i>guaranteed</i> that the sorted set cannot contain an incorrectly
* typed element.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned sorted set will be serializable if the specified sorted
* set is serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned sorted set permits insertion of null elements
* whenever the backing sorted set does.
*
* @param s the sorted set for which a dynamically typesafe view is to be
* returned
* @param type the type of element that {@code s} is permitted to hold
* @return a dynamically typesafe view of the specified sorted set
* @since 1.5
*/
public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
Class<E> type) {
return new CheckedSortedSet<>(s, type);
}
/**
* @serial include
*/
static class CheckedSortedSet<E> extends CheckedSet<E>
implements SortedSet<E>, Serializable
{
private static final long serialVersionUID = 1599911165492914959L;
private final SortedSet<E> ss;
CheckedSortedSet(SortedSet<E> s, Class<E> type) {
super(s, type);
ss = s;
}
public Comparator<? super E> comparator() { return ss.comparator(); }
public E first() { return ss.first(); }
public E last() { return ss.last(); }
public SortedSet<E> subSet(E fromElement, E toElement) {
return checkedSortedSet(ss.subSet(fromElement,toElement), type);
}
public SortedSet<E> headSet(E toElement) {
return checkedSortedSet(ss.headSet(toElement), type);
}
public SortedSet<E> tailSet(E fromElement) {
return checkedSortedSet(ss.tailSet(fromElement), type);
}
}
/**
* Returns a dynamically typesafe view of the specified list.
* Any attempt to insert an element of the wrong type will result in
* an immediate {@link ClassCastException}. Assuming a list contains
* no incorrectly typed elements prior to the time a dynamically typesafe
* view is generated, and that all subsequent access to the list
* takes place through the view, it is <i>guaranteed</i> that the
* list cannot contain an incorrectly typed element.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned list will be serializable if the specified list
* is serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned list permits insertion of null elements whenever
* the backing list does.
*
* @param list the list for which a dynamically typesafe view is to be
* returned
* @param type the type of element that {@code list} is permitted to hold
* @return a dynamically typesafe view of the specified list
* @since 1.5
*/
public static <E> List<E> checkedList(List<E> list, Class<E> type) {
return (list instanceof RandomAccess ?
new CheckedRandomAccessList<>(list, type) :
new CheckedList<>(list, type));
}
/**
* @serial include
*/
static class CheckedList<E>
extends CheckedCollection<E>
implements List<E>
{
private static final long serialVersionUID = 65247728283967356L;
final List<E> list;
CheckedList(List<E> list, Class<E> type) {
super(list, type);
this.list = list;
}
public boolean equals(Object o) { return o == this || list.equals(o); }
public int hashCode() { return list.hashCode(); }
public E get(int index) { return list.get(index); }
public E remove(int index) { return list.remove(index); }
public int indexOf(Object o) { return list.indexOf(o); }
public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
public E set(int index, E element) {
typeCheck(element);
return list.set(index, element);
}
public void add(int index, E element) {
typeCheck(element);
list.add(index, element);
}
public boolean addAll(int index, Collection<? extends E> c) {
return list.addAll(index, checkedCopyOf(c));
}
public ListIterator<E> listIterator() { return listIterator(0); }
public ListIterator<E> listIterator(final int index) {
final ListIterator<E> i = list.listIterator(index);
return new ListIterator<E>() {
public boolean hasNext() { return i.hasNext(); }
public E next() { return i.next(); }
public boolean hasPrevious() { return i.hasPrevious(); }
public E previous() { return i.previous(); }
public int nextIndex() { return i.nextIndex(); }
public int previousIndex() { return i.previousIndex(); }
public void remove() { i.remove(); }
public void set(E e) {
typeCheck(e);
i.set(e);
}
public void add(E e) {
typeCheck(e);
i.add(e);
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new CheckedList<>(list.subList(fromIndex, toIndex), type);
}
}
/**
* @serial include
*/
static class CheckedRandomAccessList<E> extends CheckedList<E>
implements RandomAccess
{
private static final long serialVersionUID = 1638200125423088369L;
CheckedRandomAccessList(List<E> list, Class<E> type) {
super(list, type);
}
public List<E> subList(int fromIndex, int toIndex) {
return new CheckedRandomAccessList<>(
list.subList(fromIndex, toIndex), type);
}
}
/**
* Returns a dynamically typesafe view of the specified map.
* Any attempt to insert a mapping whose key or value have the wrong
* type will result in an immediate {@link ClassCastException}.
* Similarly, any attempt to modify the value currently associated with
* a key will result in an immediate {@link ClassCastException},
* whether the modification is attempted directly through the map
* itself, or through a {@link Map.Entry} instance obtained from the
* map's {@link Map#entrySet() entry set} view.
*
* <p>Assuming a map contains no incorrectly typed keys or values
* prior to the time a dynamically typesafe view is generated, and
* that all subsequent access to the map takes place through the view
* (or one of its collection views), it is <i>guaranteed</i> that the
* map cannot contain an incorrectly typed key or value.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned map will be serializable if the specified map is
* serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned map permits insertion of null keys or values
* whenever the backing map does.
*
* @param m the map for which a dynamically typesafe view is to be
* returned
* @param keyType the type of key that {@code m} is permitted to hold
* @param valueType the type of value that {@code m} is permitted to hold
* @return a dynamically typesafe view of the specified map
* @since 1.5
*/
public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
Class<K> keyType,
Class<V> valueType) {
return new CheckedMap<>(m, keyType, valueType);
}
/**
* @serial include
*/
private static class CheckedMap<K,V>
implements Map<K,V>, Serializable
{
private static final long serialVersionUID = 5742860141034234728L;
private final Map<K, V> m;
final Class<K> keyType;
final Class<V> valueType;
private void typeCheck(Object key, Object value) {
if (key != null && !keyType.isInstance(key))
throw new ClassCastException(badKeyMsg(key));
if (value != null && !valueType.isInstance(value))
throw new ClassCastException(badValueMsg(value));
}
private String badKeyMsg(Object key) {
return "Attempt to insert " + key.getClass() +
" key into map with key type " + keyType;
}
private String badValueMsg(Object value) {
return "Attempt to insert " + value.getClass() +
" value into map with value type " + valueType;
}
CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
if (m == null || keyType == null || valueType == null)
throw new NullPointerException();
this.m = m;
this.keyType = keyType;
this.valueType = valueType;
}
public int size() { return m.size(); }
public boolean isEmpty() { return m.isEmpty(); }
public boolean containsKey(Object key) { return m.containsKey(key); }
public boolean containsValue(Object v) { return m.containsValue(v); }
public V get(Object key) { return m.get(key); }
public V remove(Object key) { return m.remove(key); }
public void clear() { m.clear(); }
public Set<K> keySet() { return m.keySet(); }
public Collection<V> values() { return m.values(); }
public boolean equals(Object o) { return o == this || m.equals(o); }
public int hashCode() { return m.hashCode(); }
public String toString() { return m.toString(); }
public V put(K key, V value) {
typeCheck(key, value);
return m.put(key, value);
}
@SuppressWarnings("unchecked")
public void putAll(Map<? extends K, ? extends V> t) {
// Satisfy the following goals:
// - good diagnostics in case of type mismatch
// - all-or-nothing semantics
// - protection from malicious t
// - correct behavior if t is a concurrent map
Object[] entries = t.entrySet().toArray();
List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
for (Object o : entries) {
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object k = e.getKey();
Object v = e.getValue();
typeCheck(k, v);
checked.add(
new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v));
}
for (Map.Entry<K,V> e : checked)
m.put(e.getKey(), e.getValue());
}
private transient Set<Map.Entry<K,V>> entrySet = null;
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
return entrySet;
}
// Override default methods in Map
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
m.forEach(action);
}
/**
* We need this class in addition to CheckedSet as Map.Entry permits
* modification of the backing Map via the setValue operation. This
* class is subtle: there are many possible attacks that must be
* thwarted.
*
* @serial exclude
*/
static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
private final Set<Map.Entry<K,V>> s;
private final Class<V> valueType;
CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
this.s = s;
this.valueType = valueType;
}
public int size() { return s.size(); }
public boolean isEmpty() { return s.isEmpty(); }
public String toString() { return s.toString(); }
public int hashCode() { return s.hashCode(); }
public void clear() { s.clear(); }
public boolean add(Map.Entry<K, V> e) {
throw new UnsupportedOperationException();
}
public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
throw new UnsupportedOperationException();
}
public Iterator<Map.Entry<K,V>> iterator() {
final Iterator<Map.Entry<K, V>> i = s.iterator();
final Class<V> valueType = this.valueType;
return new Iterator<Map.Entry<K,V>>() {
public boolean hasNext() { return i.hasNext(); }
public void remove() { i.remove(); }
public Map.Entry<K,V> next() {
return checkedEntry(i.next(), valueType);
}
};
}
@SuppressWarnings("unchecked")
public Object[] toArray() {
Object[] source = s.toArray();
/*
* Ensure that we don't get an ArrayStoreException even if
* s.toArray returns an array of something other than Object
*/
Object[] dest = (CheckedEntry.class.isInstance(
source.getClass().getComponentType()) ? source :
new Object[source.length]);
for (int i = 0; i < source.length; i++)
dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
valueType);
return dest;
}
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
// We don't pass a to s.toArray, to avoid window of
// vulnerability wherein an unscrupulous multithreaded client
// could get his hands on raw (unwrapped) Entries from s.
T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
for (int i=0; i<arr.length; i++)
arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
valueType);
if (arr.length > a.length)
return arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
/**
* This method is overridden to protect the backing set against
* an object with a nefarious equals function that senses
* that the equality-candidate is Map.Entry and calls its
* setValue method.
*/
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
return s.contains(
(e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
}
/**
* The bulk collection methods are overridden to protect
* against an unscrupulous collection whose contains(Object o)
* method senses when o is a Map.Entry, and calls o.setValue.
*/
public boolean containsAll(Collection<?> c) {
for (Object o : c)
if (!contains(o)) // Invokes safe contains() above
return false;
return true;
}
public boolean remove(Object o) {
if (!(o instanceof Map.Entry))
return false;
return s.remove(new AbstractMap.SimpleImmutableEntry
<>((Map.Entry<?,?>)o));
}
public boolean removeAll(Collection<?> c) {
return batchRemove(c, false);
}
public boolean retainAll(Collection<?> c) {
return batchRemove(c, true);
}
private boolean batchRemove(Collection<?> c, boolean complement) {
boolean modified = false;
Iterator<Map.Entry<K,V>> it = iterator();
while (it.hasNext()) {
if (c.contains(it.next()) != complement) {
it.remove();
modified = true;
}
}
return modified;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set<?> that = (Set<?>) o;
return that.size() == s.size()
&& containsAll(that); // Invokes safe containsAll() above
}
static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
Class<T> valueType) {
return new CheckedEntry<>(e, valueType);
}
/**
* This "wrapper class" serves two purposes: it prevents
* the client from modifying the backing Map, by short-circuiting
* the setValue method, and it protects the backing Map against
* an ill-behaved Map.Entry that attempts to modify another
* Map.Entry when asked to perform an equality check.
*/
private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
private final Map.Entry<K, V> e;
private final Class<T> valueType;
CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
this.e = e;
this.valueType = valueType;
}
public K getKey() { return e.getKey(); }
public V getValue() { return e.getValue(); }
public int hashCode() { return e.hashCode(); }
public String toString() { return e.toString(); }
public V setValue(V value) {
if (value != null && !valueType.isInstance(value))
throw new ClassCastException(badValueMsg(value));
return e.setValue(value);
}
private String badValueMsg(Object value) {
return "Attempt to insert " + value.getClass() +
" value into map with value type " + valueType;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map.Entry))
return false;
return e.equals(new AbstractMap.SimpleImmutableEntry
<>((Map.Entry<?,?>)o));
}
}
}
}
/**
* Returns a dynamically typesafe view of the specified sorted map.
* Any attempt to insert a mapping whose key or value have the wrong
* type will result in an immediate {@link ClassCastException}.
* Similarly, any attempt to modify the value currently associated with
* a key will result in an immediate {@link ClassCastException},
* whether the modification is attempted directly through the map
* itself, or through a {@link Map.Entry} instance obtained from the
* map's {@link Map#entrySet() entry set} view.
*
* <p>Assuming a map contains no incorrectly typed keys or values
* prior to the time a dynamically typesafe view is generated, and
* that all subsequent access to the map takes place through the view
* (or one of its collection views), it is <i>guaranteed</i> that the
* map cannot contain an incorrectly typed key or value.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned map will be serializable if the specified map is
* serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned map permits insertion of null keys or values
* whenever the backing map does.
*
* @param m the map for which a dynamically typesafe view is to be
* returned
* @param keyType the type of key that {@code m} is permitted to hold
* @param valueType the type of value that {@code m} is permitted to hold
* @return a dynamically typesafe view of the specified map
* @since 1.5
*/
public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
Class<K> keyType,
Class<V> valueType) {
return new CheckedSortedMap<>(m, keyType, valueType);
}
/**
* @serial include
*/
static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
implements SortedMap<K,V>, Serializable
{
private static final long serialVersionUID = 1599671320688067438L;
private final SortedMap<K, V> sm;
CheckedSortedMap(SortedMap<K, V> m,
Class<K> keyType, Class<V> valueType) {
super(m, keyType, valueType);
sm = m;
}
public Comparator<? super K> comparator() { return sm.comparator(); }
public K firstKey() { return sm.firstKey(); }
public K lastKey() { return sm.lastKey(); }
public SortedMap<K,V> subMap(K fromKey, K toKey) {
return checkedSortedMap(sm.subMap(fromKey, toKey),
keyType, valueType);
}
public SortedMap<K,V> headMap(K toKey) {
return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
}
public SortedMap<K,V> tailMap(K fromKey) {
return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
}
}
// Empty collections
/**
* Returns an iterator that has no elements. More precisely,
*
* <ul compact>
*
* <li>{@link Iterator#hasNext hasNext} always returns {@code
* false}.
*
* <li>{@link Iterator#next next} always throws {@link
* NoSuchElementException}.
*
* <li>{@link Iterator#remove remove} always throws {@link
* IllegalStateException}.
*
* </ul>
*
* <p>Implementations of this method are permitted, but not
* required, to return the same object from multiple invocations.
*
* @return an empty iterator
* @since 1.7
*/
@SuppressWarnings("unchecked")
public static <T> Iterator<T> emptyIterator() {
return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
}
private static class EmptyIterator<E> implements Iterator<E> {
static final EmptyIterator<Object> EMPTY_ITERATOR
= new EmptyIterator<>();
public boolean hasNext() { return false; }
public E next() { throw new NoSuchElementException(); }
public void remove() { throw new IllegalStateException(); }
}
/**
* Returns a list iterator that has no elements. More precisely,
*
* <ul compact>
*
* <li>{@link Iterator#hasNext hasNext} and {@link
* ListIterator#hasPrevious hasPrevious} always return {@code
* false}.
*
* <li>{@link Iterator#next next} and {@link ListIterator#previous
* previous} always throw {@link NoSuchElementException}.
*
* <li>{@link Iterator#remove remove} and {@link ListIterator#set
* set} always throw {@link IllegalStateException}.
*
* <li>{@link ListIterator#add add} always throws {@link
* UnsupportedOperationException}.
*
* <li>{@link ListIterator#nextIndex nextIndex} always returns
* {@code 0} .
*
* <li>{@link ListIterator#previousIndex previousIndex} always
* returns {@code -1}.
*
* </ul>
*
* <p>Implementations of this method are permitted, but not
* required, to return the same object from multiple invocations.
*
* @return an empty list iterator
* @since 1.7
*/
@SuppressWarnings("unchecked")
public static <T> ListIterator<T> emptyListIterator() {
return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
}
private static class EmptyListIterator<E>
extends EmptyIterator<E>
implements ListIterator<E>
{
static final EmptyListIterator<Object> EMPTY_ITERATOR
= new EmptyListIterator<>();
public boolean hasPrevious() { return false; }
public E previous() { throw new NoSuchElementException(); }
public int nextIndex() { return 0; }
public int previousIndex() { return -1; }
public void set(E e) { throw new IllegalStateException(); }
public void add(E e) { throw new UnsupportedOperationException(); }
}
/**
* Returns an enumeration that has no elements. More precisely,
*
* <ul compact>
*
* <li>{@link Enumeration#hasMoreElements hasMoreElements} always
* returns {@code false}.
*
* <li> {@link Enumeration#nextElement nextElement} always throws
* {@link NoSuchElementException}.
*
* </ul>
*
* <p>Implementations of this method are permitted, but not
* required, to return the same object from multiple invocations.
*
* @return an empty enumeration
* @since 1.7
*/
@SuppressWarnings("unchecked")
public static <T> Enumeration<T> emptyEnumeration() {
return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
}
private static class EmptyEnumeration<E> implements Enumeration<E> {
static final EmptyEnumeration<Object> EMPTY_ENUMERATION
= new EmptyEnumeration<>();
public boolean hasMoreElements() { return false; }
public E nextElement() { throw new NoSuchElementException(); }
}
/**
* The empty set (immutable). This set is serializable.
*
* @see #emptySet()
*/
@SuppressWarnings("unchecked")
public static final Set EMPTY_SET = new EmptySet<>();
/**
* Returns the empty set (immutable). This set is serializable.
* Unlike the like-named field, this method is parameterized.
*
* <p>This example illustrates the type-safe way to obtain an empty set:
* <pre>
* Set&lt;String&gt; s = Collections.emptySet();
* </pre>
* Implementation note: Implementations of this method need not
* create a separate <tt>Set</tt> object for each call. Using this
* method is likely to have comparable cost to using the like-named
* field. (Unlike this method, the field does not provide type safety.)
*
* @see #EMPTY_SET
* @since 1.5
*/
@SuppressWarnings("unchecked")
public static final <T> Set<T> emptySet() {
return (Set<T>) EMPTY_SET;
}
/**
* @serial include
*/
private static class EmptySet<E>
extends AbstractSet<E>
implements Serializable
{
private static final long serialVersionUID = 1582296315990362920L;
public Iterator<E> iterator() { return emptyIterator(); }
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean contains(Object obj) {return false;}
public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
public Object[] toArray() { return new Object[0]; }
public <T> T[] toArray(T[] a) {
if (a.length > 0)
a[0] = null;
return a;
}
// Preserves singleton property
private Object readResolve() {
return EMPTY_SET;
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
}
}
/**
* The empty list (immutable). This list is serializable.
*
* @see #emptyList()
*/
@SuppressWarnings("unchecked")
public static final List EMPTY_LIST = new EmptyList<>();
/**
* Returns the empty list (immutable). This list is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty list:
* <pre>
* List&lt;String&gt; s = Collections.emptyList();
* </pre>
* Implementation note: Implementations of this method need not
* create a separate <tt>List</tt> object for each call. Using this
* method is likely to have comparable cost to using the like-named
* field. (Unlike this method, the field does not provide type safety.)
*
* @see #EMPTY_LIST
* @since 1.5
*/
@SuppressWarnings("unchecked")
public static final <T> List<T> emptyList() {
return (List<T>) EMPTY_LIST;
}
/**
* @serial include
*/
private static class EmptyList<E>
extends AbstractList<E>
implements RandomAccess, Serializable {
private static final long serialVersionUID = 8842843931221139166L;
public Iterator<E> iterator() {
return emptyIterator();
}
public ListIterator<E> listIterator() {
return emptyListIterator();
}
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean contains(Object obj) {return false;}
public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
public Object[] toArray() { return new Object[0]; }
public <T> T[] toArray(T[] a) {
if (a.length > 0)
a[0] = null;
return a;
}
public E get(int index) {
throw new IndexOutOfBoundsException("Index: "+index);
}
public boolean equals(Object o) {
return (o instanceof List) && ((List<?>)o).isEmpty();
}
public int hashCode() { return 1; }
// Preserves singleton property
private Object readResolve() {
return EMPTY_LIST;
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
}
}
/**
* The empty map (immutable). This map is serializable.
*
* @see #emptyMap()
* @since 1.3
*/
@SuppressWarnings("unchecked")
public static final Map EMPTY_MAP = new EmptyMap<>();
/**
* Returns the empty map (immutable). This map is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty set:
* <pre>
* Map&lt;String, Date&gt; s = Collections.emptyMap();
* </pre>
* Implementation note: Implementations of this method need not
* create a separate <tt>Map</tt> object for each call. Using this
* method is likely to have comparable cost to using the like-named
* field. (Unlike this method, the field does not provide type safety.)
*
* @see #EMPTY_MAP
* @since 1.5
*/
@SuppressWarnings("unchecked")
public static final <K,V> Map<K,V> emptyMap() {
return (Map<K,V>) EMPTY_MAP;
}
/**
* @serial include
*/
private static class EmptyMap<K,V>
extends AbstractMap<K,V>
implements Serializable
{
private static final long serialVersionUID = 6428348081105594320L;
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean containsKey(Object key) {return false;}
public boolean containsValue(Object value) {return false;}
public V get(Object key) {return null;}
public Set<K> keySet() {return emptySet();}
public Collection<V> values() {return emptySet();}
public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
public boolean equals(Object o) {
return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
}
public int hashCode() {return 0;}
// Preserves singleton property
private Object readResolve() {
return EMPTY_MAP;
}
// Override default methods in Map
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
Objects.requireNonNull(action);
}
}
// Singleton collections
/**
* Returns an immutable set containing only the specified object.
* The returned set is serializable.
*
* @param o the sole object to be stored in the returned set.
* @return an immutable set containing only the specified object.
*/
public static <E> Set<E> singleton(E o) {
return new SingletonSet<>(o);
}
static <E> Iterator<E> singletonIterator(final E e) {
return new Iterator<E>() {
private boolean hasNext = true;
public boolean hasNext() {
return hasNext;
}
public E next() {
if (hasNext) {
hasNext = false;
return e;
}
throw new NoSuchElementException();
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
/**
* @serial include
*/
private static class SingletonSet<E>
extends AbstractSet<E>
implements Serializable
{
private static final long serialVersionUID = 3193687207550431679L;
private final E element;
SingletonSet(E e) {element = e;}
public Iterator<E> iterator() {
return singletonIterator(element);
}
public int size() {return 1;}
public boolean contains(Object o) {return eq(o, element);}
// Override default methods for Collection
@Override
public void forEach(Consumer<? super E> action) {
action.accept(element);
}
}
/**
* Returns an immutable list containing only the specified object.
* The returned list is serializable.
*
* @param o the sole object to be stored in the returned list.
* @return an immutable list containing only the specified object.
* @since 1.3
*/
public static <E> List<E> singletonList(E o) {
return new SingletonList<>(o);
}
/**
* @serial include
*/
private static class SingletonList<E>
extends AbstractList<E>
implements RandomAccess, Serializable {
private static final long serialVersionUID = 3093736618740652951L;
private final E element;
SingletonList(E obj) {element = obj;}
public Iterator<E> iterator() {
return singletonIterator(element);
}
public int size() {return 1;}
public boolean contains(Object obj) {return eq(obj, element);}
public E get(int index) {
if (index != 0)
throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
return element;
}
// Override default methods for Collection
@Override
public void forEach(Consumer<? super E> action) {
action.accept(element);
}
}
/**
* Returns an immutable map, mapping only the specified key to the
* specified value. The returned map is serializable.
*
* @param key the sole key to be stored in the returned map.
* @param value the value to which the returned map maps <tt>key</tt>.
* @return an immutable map containing only the specified key-value
* mapping.
* @since 1.3
*/
public static <K,V> Map<K,V> singletonMap(K key, V value) {
return new SingletonMap<>(key, value);
}
/**
* @serial include
*/
private static class SingletonMap<K,V>
extends AbstractMap<K,V>
implements Serializable {
private static final long serialVersionUID = -6979724477215052911L;
private final K k;
private final V v;
SingletonMap(K key, V value) {
k = key;
v = value;
}
public int size() {return 1;}
public boolean isEmpty() {return false;}
public boolean containsKey(Object key) {return eq(key, k);}
public boolean containsValue(Object value) {return eq(value, v);}
public V get(Object key) {return (eq(key, k) ? v : null);}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;
public Set<K> keySet() {
if (keySet==null)
keySet = singleton(k);
return keySet;
}
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = Collections.<Map.Entry<K,V>>singleton(
new SimpleImmutableEntry<>(k, v));
return entrySet;
}
public Collection<V> values() {
if (values==null)
values = singleton(v);
return values;
}
// Override default methods in Map
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
action.accept(k, v);
}
}
// Miscellaneous
/**
* Returns an immutable list consisting of <tt>n</tt> copies of the
* specified object. The newly allocated data object is tiny (it contains
* a single reference to the data object). This method is useful in
* combination with the <tt>List.addAll</tt> method to grow lists.
* The returned list is serializable.
*
* @param n the number of elements in the returned list.
* @param o the element to appear repeatedly in the returned list.
* @return an immutable list consisting of <tt>n</tt> copies of the
* specified object.
* @throws IllegalArgumentException if {@code n < 0}
* @see List#addAll(Collection)
* @see List#addAll(int, Collection)
*/
public static <T> List<T> nCopies(int n, T o) {
if (n < 0)
throw new IllegalArgumentException("List length = " + n);
return new CopiesList<>(n, o);
}
/**
* @serial include
*/
private static class CopiesList<E>
extends AbstractList<E>
implements RandomAccess, Serializable
{
private static final long serialVersionUID = 2739099268398711800L;
final int n;
final E element;
CopiesList(int n, E e) {
assert n >= 0;
this.n = n;
element = e;
}
public int size() {
return n;
}
public boolean contains(Object obj) {
return n != 0 && eq(obj, element);
}
public int indexOf(Object o) {
return contains(o) ? 0 : -1;
}
public int lastIndexOf(Object o) {
return contains(o) ? n - 1 : -1;
}
public E get(int index) {
if (index < 0 || index >= n)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+n);
return element;
}
public Object[] toArray() {
final Object[] a = new Object[n];
if (element != null)
Arrays.fill(a, 0, n, element);
return a;
}
public <T> T[] toArray(T[] a) {
final int n = this.n;
if (a.length < n) {
a = (T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), n);
if (element != null)
Arrays.fill(a, 0, n, element);
} else {
Arrays.fill(a, 0, n, element);
if (a.length > n)
a[n] = null;
}
return a;
}
public List<E> subList(int fromIndex, int toIndex) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > n)
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
return new CopiesList<>(toIndex - fromIndex, element);
}
}
/**
* Returns a comparator that imposes the reverse of the <em>natural
* ordering</em> on a collection of objects that implement the
* {@code Comparable} interface. (The natural ordering is the ordering
* imposed by the objects' own {@code compareTo} method.) This enables a
* simple idiom for sorting (or maintaining) collections (or arrays) of
* objects that implement the {@code Comparable} interface in
* reverse-natural-order. For example, suppose {@code a} is an array of
* strings. Then: <pre>
* Arrays.sort(a, Collections.reverseOrder());
* </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
*
* The returned comparator is serializable.
*
* @return A comparator that imposes the reverse of the <i>natural
* ordering</i> on a collection of objects that implement
* the <tt>Comparable</tt> interface.
* @see Comparable
*/
public static <T> Comparator<T> reverseOrder() {
return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
}
/**
* @serial include
*/
private static class ReverseComparator
implements Comparator<Comparable<Object>>, Serializable {
private static final long serialVersionUID = 7207038068494060240L;
static final ReverseComparator REVERSE_ORDER
= new ReverseComparator();
public int compare(Comparable<Object> c1, Comparable<Object> c2) {
return c2.compareTo(c1);
}
private Object readResolve() { return reverseOrder(); }
}
/**
* Returns a comparator that imposes the reverse ordering of the specified
* comparator. If the specified comparator is {@code null}, this method is
* equivalent to {@link #reverseOrder()} (in other words, it returns a
* comparator that imposes the reverse of the <em>natural ordering</em> on
* a collection of objects that implement the Comparable interface).
*
* <p>The returned comparator is serializable (assuming the specified
* comparator is also serializable or {@code null}).
*
* @param cmp a comparator who's ordering is to be reversed by the returned
* comparator or {@code null}
* @return A comparator that imposes the reverse ordering of the
* specified comparator.
* @since 1.5
*/
public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
if (cmp == null)
return reverseOrder();
if (cmp instanceof ReverseComparator2)
return ((ReverseComparator2<T>)cmp).cmp;
return new ReverseComparator2<>(cmp);
}
/**
* @serial include
*/
private static class ReverseComparator2<T> implements Comparator<T>,
Serializable
{
private static final long serialVersionUID = 4374092139857L;
/**
* The comparator specified in the static factory. This will never
* be null, as the static factory returns a ReverseComparator
* instance if its argument is null.
*
* @serial
*/
final Comparator<T> cmp;
ReverseComparator2(Comparator<T> cmp) {
assert cmp != null;
this.cmp = cmp;
}
public int compare(T t1, T t2) {
return cmp.compare(t2, t1);
}
public boolean equals(Object o) {
return (o == this) ||
(o instanceof ReverseComparator2 &&
cmp.equals(((ReverseComparator2)o).cmp));
}
public int hashCode() {
return cmp.hashCode() ^ Integer.MIN_VALUE;
}
}
/**
* Returns an enumeration over the specified collection. This provides
* interoperability with legacy APIs that require an enumeration
* as input.
*
* @param c the collection for which an enumeration is to be returned.
* @return an enumeration over the specified collection.
* @see Enumeration
*/
public static <T> Enumeration<T> enumeration(final Collection<T> c) {
return new Enumeration<T>() {
private final Iterator<T> i = c.iterator();
public boolean hasMoreElements() {
return i.hasNext();
}
public T nextElement() {
return i.next();
}
};
}
/**
* Returns an array list containing the elements returned by the
* specified enumeration in the order they are returned by the
* enumeration. This method provides interoperability between
* legacy APIs that return enumerations and new APIs that require
* collections.
*
* @param e enumeration providing elements for the returned
* array list
* @return an array list containing the elements returned
* by the specified enumeration.
* @since 1.4
* @see Enumeration
* @see ArrayList
*/
public static <T> ArrayList<T> list(Enumeration<T> e) {
ArrayList<T> l = new ArrayList<>();
while (e.hasMoreElements())
l.add(e.nextElement());
return l;
}
/**
* Returns true if the specified arguments are equal, or both null.
*/
static boolean eq(Object o1, Object o2) {
return o1==null ? o2==null : o1.equals(o2);
}
/**
* Returns the number of elements in the specified collection equal to the
* specified object. More formally, returns the number of elements
* <tt>e</tt> in the collection such that
* <tt>(o == null ? e == null : o.equals(e))</tt>.
*
* @param c the collection in which to determine the frequency
* of <tt>o</tt>
* @param o the object whose frequency is to be determined
* @throws NullPointerException if <tt>c</tt> is null
* @since 1.5
*/
public static int frequency(Collection<?> c, Object o) {
int result = 0;
if (o == null) {
for (Object e : c)
if (e == null)
result++;
} else {
for (Object e : c)
if (o.equals(e))
result++;
}
return result;
}
/**
* Returns {@code true} if the two specified collections have no
* elements in common.
*
* <p>Care must be exercised if this method is used on collections that
* do not comply with the general contract for {@code Collection}.
* Implementations may elect to iterate over either collection and test
* for containment in the other collection (or to perform any equivalent
* computation). If either collection uses a nonstandard equality test
* (as does a {@link SortedSet} whose ordering is not <em>compatible with
* equals</em>, or the key set of an {@link IdentityHashMap}), both
* collections must use the same nonstandard equality test, or the
* result of this method is undefined.
*
* <p>Care must also be exercised when using collections that have
* restrictions on the elements that they may contain. Collection
* implementations are allowed to throw exceptions for any operation
* involving elements they deem ineligible. For absolute safety the
* specified collections should contain only elements which are
* eligible elements for both collections.
*
* <p>Note that it is permissible to pass the same collection in both
* parameters, in which case the method will return {@code true} if and
* only if the collection is empty.
*
* @param c1 a collection
* @param c2 a collection
* @return {@code true} if the two specified collections have no
* elements in common.
* @throws NullPointerException if either collection is {@code null}.
* @throws NullPointerException if one collection contains a {@code null}
* element and {@code null} is not an eligible element for the other collection.
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if one collection contains an element that is
* of a type which is ineligible for the other collection.
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @since 1.5
*/
public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
// The collection to be used for contains(). Preference is given to
// the collection who's contains() has lower O() complexity.
Collection<?> contains = c2;
// The collection to be iterated. If the collections' contains() impl
// are of different O() complexity, the collection with slower
// contains() will be used for iteration. For collections who's
// contains() are of the same complexity then best performance is
// achieved by iterating the smaller collection.
Collection<?> iterate = c1;
// Performance optimization cases. The heuristics:
// 1. Generally iterate over c1.
// 2. If c1 is a Set then iterate over c2.
// 3. If either collection is empty then result is always true.
// 4. Iterate over the smaller Collection.
if (c1 instanceof Set) {
// Use c1 for contains as a Set's contains() is expected to perform
// better than O(N/2)
iterate = c2;
contains = c1;
} else if (!(c2 instanceof Set)) {
// Both are mere Collections. Iterate over smaller collection.
// Example: If c1 contains 3 elements and c2 contains 50 elements and
// assuming contains() requires ceiling(N/2) comparisons then
// checking for all c1 elements in c2 would require 75 comparisons
// (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
// 100 comparisons (50 * ceiling(3/2)).
int c1size = c1.size();
int c2size = c2.size();
if (c1size == 0 || c2size == 0) {
// At least one collection is empty. Nothing will match.
return true;
}
if (c1size > c2size) {
iterate = c2;
contains = c1;
}
}
for (Object e : iterate) {
if (contains.contains(e)) {
// Found a common element. Collections are not disjoint.
return false;
}
}
// No common elements were found.
return true;
}
/**
* Adds all of the specified elements to the specified collection.
* Elements to be added may be specified individually or as an array.
* The behavior of this convenience method is identical to that of
* <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
* to run significantly faster under most implementations.
*
* <p>When elements are specified individually, this method provides a
* convenient way to add a few elements to an existing collection:
* <pre>
* Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
* </pre>
*
* @param c the collection into which <tt>elements</tt> are to be inserted
* @param elements the elements to insert into <tt>c</tt>
* @return <tt>true</tt> if the collection changed as a result of the call
* @throws UnsupportedOperationException if <tt>c</tt> does not support
* the <tt>add</tt> operation
* @throws NullPointerException if <tt>elements</tt> contains one or more
* null values and <tt>c</tt> does not permit null elements, or
* if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
* @throws IllegalArgumentException if some property of a value in
* <tt>elements</tt> prevents it from being added to <tt>c</tt>
* @see Collection#addAll(Collection)
* @since 1.5
*/
@SafeVarargs
public static <T> boolean addAll(Collection<? super T> c, T... elements) {
boolean result = false;
for (T element : elements)
result |= c.add(element);
return result;
}
/**
* Returns a set backed by the specified map. The resulting set displays
* the same ordering, concurrency, and performance characteristics as the
* backing map. In essence, this factory method provides a {@link Set}
* implementation corresponding to any {@link Map} implementation. There
* is no need to use this method on a {@link Map} implementation that
* already has a corresponding {@link Set} implementation (such as {@link
* HashMap} or {@link TreeMap}).
*
* <p>Each method invocation on the set returned by this method results in
* exactly one method invocation on the backing map or its <tt>keySet</tt>
* view, with one exception. The <tt>addAll</tt> method is implemented
* as a sequence of <tt>put</tt> invocations on the backing map.
*
* <p>The specified map must be empty at the time this method is invoked,
* and should not be accessed directly after this method returns. These
* conditions are ensured if the map is created empty, passed directly
* to this method, and no reference to the map is retained, as illustrated
* in the following code fragment:
* <pre>
* Set&lt;Object&gt; weakHashSet = Collections.newSetFromMap(
* new WeakHashMap&lt;Object, Boolean&gt;());
* </pre>
*
* @param map the backing map
* @return the set backed by the map
* @throws IllegalArgumentException if <tt>map</tt> is not empty
* @since 1.6
*/
public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
return new SetFromMap<>(map);
}
/**
* @serial include
*/
private static class SetFromMap<E> extends AbstractSet<E>
implements Set<E>, Serializable
{
private final Map<E, Boolean> m; // The backing map
private transient Set<E> s; // Its keySet
SetFromMap(Map<E, Boolean> map) {
if (!map.isEmpty())
throw new IllegalArgumentException("Map is non-empty");
m = map;
s = map.keySet();
}
public void clear() { m.clear(); }
public int size() { return m.size(); }
public boolean isEmpty() { return m.isEmpty(); }
public boolean contains(Object o) { return m.containsKey(o); }
public boolean remove(Object o) { return m.remove(o) != null; }
public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
public Iterator<E> iterator() { return s.iterator(); }
public Object[] toArray() { return s.toArray(); }
public <T> T[] toArray(T[] a) { return s.toArray(a); }
public String toString() { return s.toString(); }
public int hashCode() { return s.hashCode(); }
public boolean equals(Object o) { return o == this || s.equals(o); }
public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
// addAll is the only inherited implementation
private static final long serialVersionUID = 2454657854757543876L;
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
s.forEach(action);
}
private void readObject(java.io.ObjectInputStream stream)
throws IOException, ClassNotFoundException
{
stream.defaultReadObject();
s = m.keySet();
}
}
/**
* Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
* {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
* <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
* view can be useful when you would like to use a method
* requiring a <tt>Queue</tt> but you need Lifo ordering.
*
* <p>Each method invocation on the queue returned by this method
* results in exactly one method invocation on the backing deque, with
* one exception. The {@link Queue#addAll addAll} method is
* implemented as a sequence of {@link Deque#addFirst addFirst}
* invocations on the backing deque.
*
* @param deque the deque
* @return the queue
* @since 1.6
*/
public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
return new AsLIFOQueue<>(deque);
}
/**
* @serial include
*/
static class AsLIFOQueue<E> extends AbstractQueue<E>
implements Queue<E>, Serializable {
private static final long serialVersionUID = 1802017725587941708L;
private final Deque<E> q;
AsLIFOQueue(Deque<E> q) { this.q = q; }
public boolean add(E e) { q.addFirst(e); return true; }
public boolean offer(E e) { return q.offerFirst(e); }
public E poll() { return q.pollFirst(); }
public E remove() { return q.removeFirst(); }
public E peek() { return q.peekFirst(); }
public E element() { return q.getFirst(); }
public void clear() { q.clear(); }
public int size() { return q.size(); }
public boolean isEmpty() { return q.isEmpty(); }
public boolean contains(Object o) { return q.contains(o); }
public boolean remove(Object o) { return q.remove(o); }
public Iterator<E> iterator() { return q.iterator(); }
public Object[] toArray() { return q.toArray(); }
public <T> T[] toArray(T[] a) { return q.toArray(a); }
public String toString() { return q.toString(); }
public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
// We use inherited addAll; forwarding addAll would be wrong
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {q.forEach(action);}
}
}