| /* |
| * Copyright (c) 1997, 2013, 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; |
| |
| /** |
| * This class implements the <tt>Set</tt> interface, backed by a hash table |
| * (actually a <tt>HashMap</tt> instance). It makes no guarantees as to the |
| * iteration order of the set; in particular, it does not guarantee that the |
| * order will remain constant over time. This class permits the <tt>null</tt> |
| * element. |
| * |
| * <p>This class offers constant time performance for the basic operations |
| * (<tt>add</tt>, <tt>remove</tt>, <tt>contains</tt> and <tt>size</tt>), |
| * assuming the hash function disperses the elements properly among the |
| * buckets. Iterating over this set requires time proportional to the sum of |
| * the <tt>HashSet</tt> instance's size (the number of elements) plus the |
| * "capacity" of the backing <tt>HashMap</tt> instance (the number of |
| * buckets). Thus, it's very important not to set the initial capacity too |
| * high (or the load factor too low) if iteration performance is important. |
| * |
| * <p><strong>Note that this implementation is not synchronized.</strong> |
| * If multiple threads access a hash set concurrently, and at least one of |
| * the threads modifies the set, it <i>must</i> be synchronized externally. |
| * This is typically accomplished by synchronizing on some object that |
| * naturally encapsulates the set. |
| * |
| * If no such object exists, the set should be "wrapped" using the |
| * {@link Collections#synchronizedSet Collections.synchronizedSet} |
| * method. This is best done at creation time, to prevent accidental |
| * unsynchronized access to the set:<pre> |
| * Set s = Collections.synchronizedSet(new HashSet(...));</pre> |
| * |
| * <p>The iterators returned by this class's <tt>iterator</tt> method are |
| * <i>fail-fast</i>: if the set is modified at any time after the iterator is |
| * created, in any way except through the iterator's own <tt>remove</tt> |
| * method, the Iterator throws a {@link ConcurrentModificationException}. |
| * Thus, in the face of concurrent modification, the iterator fails quickly |
| * and cleanly, rather than risking arbitrary, non-deterministic behavior at |
| * an undetermined time in the future. |
| * |
| * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
| * as it is, generally speaking, impossible to make any hard guarantees in the |
| * presence of unsynchronized concurrent modification. Fail-fast iterators |
| * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
| * Therefore, it would be wrong to write a program that depended on this |
| * exception for its correctness: <i>the fail-fast behavior of iterators |
| * should be used only to detect bugs.</i> |
| * |
| * <p>This class is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @param <E> the type of elements maintained by this set |
| * |
| * @author Josh Bloch |
| * @author Neal Gafter |
| * @see Collection |
| * @see Set |
| * @see TreeSet |
| * @see HashMap |
| * @since 1.2 |
| */ |
| |
| public class HashSet<E> |
| extends AbstractSet<E> |
| implements Set<E>, Cloneable, java.io.Serializable |
| { |
| static final long serialVersionUID = -5024744406713321676L; |
| |
| private transient HashMap<E,Object> map; |
| |
| // Dummy value to associate with an Object in the backing Map |
| private static final Object PRESENT = new Object(); |
| |
| /** |
| * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has |
| * default initial capacity (16) and load factor (0.75). |
| */ |
| public HashSet() { |
| map = new HashMap<>(); |
| } |
| |
| /** |
| * Constructs a new set containing the elements in the specified |
| * collection. The <tt>HashMap</tt> is created with default load factor |
| * (0.75) and an initial capacity sufficient to contain the elements in |
| * the specified collection. |
| * |
| * @param c the collection whose elements are to be placed into this set |
| * @throws NullPointerException if the specified collection is null |
| */ |
| public HashSet(Collection<? extends E> c) { |
| map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16)); |
| addAll(c); |
| } |
| |
| /** |
| * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has |
| * the specified initial capacity and the specified load factor. |
| * |
| * @param initialCapacity the initial capacity of the hash map |
| * @param loadFactor the load factor of the hash map |
| * @throws IllegalArgumentException if the initial capacity is less |
| * than zero, or if the load factor is nonpositive |
| */ |
| public HashSet(int initialCapacity, float loadFactor) { |
| map = new HashMap<>(initialCapacity, loadFactor); |
| } |
| |
| /** |
| * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has |
| * the specified initial capacity and default load factor (0.75). |
| * |
| * @param initialCapacity the initial capacity of the hash table |
| * @throws IllegalArgumentException if the initial capacity is less |
| * than zero |
| */ |
| public HashSet(int initialCapacity) { |
| map = new HashMap<>(initialCapacity); |
| } |
| |
| /** |
| * Constructs a new, empty linked hash set. (This package private |
| * constructor is only used by LinkedHashSet.) The backing |
| * HashMap instance is a LinkedHashMap with the specified initial |
| * capacity and the specified load factor. |
| * |
| * @param initialCapacity the initial capacity of the hash map |
| * @param loadFactor the load factor of the hash map |
| * @param dummy ignored (distinguishes this |
| * constructor from other int, float constructor.) |
| * @throws IllegalArgumentException if the initial capacity is less |
| * than zero, or if the load factor is nonpositive |
| */ |
| HashSet(int initialCapacity, float loadFactor, boolean dummy) { |
| map = new LinkedHashMap<>(initialCapacity, loadFactor); |
| } |
| |
| /** |
| * Returns an iterator over the elements in this set. The elements |
| * are returned in no particular order. |
| * |
| * @return an Iterator over the elements in this set |
| * @see ConcurrentModificationException |
| */ |
| public Iterator<E> iterator() { |
| return map.keySet().iterator(); |
| } |
| |
| /** |
| * Returns the number of elements in this set (its cardinality). |
| * |
| * @return the number of elements in this set (its cardinality) |
| */ |
| public int size() { |
| return map.size(); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this set contains no elements. |
| * |
| * @return <tt>true</tt> if this set contains no elements |
| */ |
| public boolean isEmpty() { |
| return map.isEmpty(); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this set contains the specified element. |
| * More formally, returns <tt>true</tt> if and only if this set |
| * contains an element <tt>e</tt> such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt>. |
| * |
| * @param o element whose presence in this set is to be tested |
| * @return <tt>true</tt> if this set contains the specified element |
| */ |
| public boolean contains(Object o) { |
| return map.containsKey(o); |
| } |
| |
| /** |
| * Adds the specified element to this set if it is not already present. |
| * More formally, adds the specified element <tt>e</tt> to this set if |
| * this set contains no element <tt>e2</tt> such that |
| * <tt>(e==null ? e2==null : e.equals(e2))</tt>. |
| * If this set already contains the element, the call leaves the set |
| * unchanged and returns <tt>false</tt>. |
| * |
| * @param e element to be added to this set |
| * @return <tt>true</tt> if this set did not already contain the specified |
| * element |
| */ |
| public boolean add(E e) { |
| return map.put(e, PRESENT)==null; |
| } |
| |
| /** |
| * Removes the specified element from this set if it is present. |
| * More formally, removes an element <tt>e</tt> such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt>, |
| * if this set contains such an element. Returns <tt>true</tt> if |
| * this set contained the element (or equivalently, if this set |
| * changed as a result of the call). (This set will not contain the |
| * element once the call returns.) |
| * |
| * @param o object to be removed from this set, if present |
| * @return <tt>true</tt> if the set contained the specified element |
| */ |
| public boolean remove(Object o) { |
| return map.remove(o)==PRESENT; |
| } |
| |
| /** |
| * Removes all of the elements from this set. |
| * The set will be empty after this call returns. |
| */ |
| public void clear() { |
| map.clear(); |
| } |
| |
| /** |
| * Returns a shallow copy of this <tt>HashSet</tt> instance: the elements |
| * themselves are not cloned. |
| * |
| * @return a shallow copy of this set |
| */ |
| public Object clone() { |
| try { |
| HashSet<E> newSet = (HashSet<E>) super.clone(); |
| newSet.map = (HashMap<E, Object>) map.clone(); |
| return newSet; |
| } catch (CloneNotSupportedException e) { |
| throw new InternalError(); |
| } |
| } |
| |
| /** |
| * Save the state of this <tt>HashSet</tt> instance to a stream (that is, |
| * serialize it). |
| * |
| * @serialData The capacity of the backing <tt>HashMap</tt> instance |
| * (int), and its load factor (float) are emitted, followed by |
| * the size of the set (the number of elements it contains) |
| * (int), followed by all of its elements (each an Object) in |
| * no particular order. |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| // Write out any hidden serialization magic |
| s.defaultWriteObject(); |
| |
| // Write out HashMap capacity and load factor |
| s.writeInt(map.capacity()); |
| s.writeFloat(map.loadFactor()); |
| |
| // Write out size |
| s.writeInt(map.size()); |
| |
| // Write out all elements in the proper order. |
| for (E e : map.keySet()) |
| s.writeObject(e); |
| } |
| |
| /** |
| * Reconstitute the <tt>HashSet</tt> instance from a stream (that is, |
| * deserialize it). |
| */ |
| private void readObject(java.io.ObjectInputStream s) |
| throws java.io.IOException, ClassNotFoundException { |
| // Read in any hidden serialization magic |
| s.defaultReadObject(); |
| |
| // Read in HashMap capacity and load factor and create backing HashMap |
| int capacity = s.readInt(); |
| float loadFactor = s.readFloat(); |
| map = (((HashSet)this) instanceof LinkedHashSet ? |
| new LinkedHashMap<E,Object>(capacity, loadFactor) : |
| new HashMap<E,Object>(capacity, loadFactor)); |
| |
| // Read in size |
| int size = s.readInt(); |
| |
| // Read in all elements in the proper order. |
| for (int i=0; i<size; i++) { |
| E e = (E) s.readObject(); |
| map.put(e, PRESENT); |
| } |
| } |
| |
| /** |
| * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> |
| * and <em>fail-fast</em> {@link Spliterator} over the elements in this |
| * set. |
| * |
| * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and |
| * {@link Spliterator#DISTINCT}. Overriding implementations should document |
| * the reporting of additional characteristic values. |
| * |
| * @return a {@code Spliterator} over the elements in this set |
| * @since 1.8 |
| */ |
| public Spliterator<E> spliterator() { |
| return new HashMap.KeySpliterator<E,Object>(map, 0, -1, 0, 0); |
| } |
| } |