| /* |
| * Copyright (C) 2014 The Android Open Source Project |
| * Copyright (c) 2000, 2010, 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.*; |
| import java.util.function.Consumer; |
| import java.util.function.BiConsumer; |
| |
| /** |
| * <p>Hash table and linked list implementation of the <tt>Map</tt> interface, |
| * with predictable iteration order. This implementation differs from |
| * <tt>HashMap</tt> in that it maintains a doubly-linked list running through |
| * all of its entries. This linked list defines the iteration ordering, |
| * which is normally the order in which keys were inserted into the map |
| * (<i>insertion-order</i>). Note that insertion order is not affected |
| * if a key is <i>re-inserted</i> into the map. (A key <tt>k</tt> is |
| * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when |
| * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to |
| * the invocation.) |
| * |
| * <p>This implementation spares its clients from the unspecified, generally |
| * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}), |
| * without incurring the increased cost associated with {@link TreeMap}. It |
| * can be used to produce a copy of a map that has the same order as the |
| * original, regardless of the original map's implementation: |
| * <pre> |
| * void foo(Map m) { |
| * Map copy = new LinkedHashMap(m); |
| * ... |
| * } |
| * </pre> |
| * This technique is particularly useful if a module takes a map on input, |
| * copies it, and later returns results whose order is determined by that of |
| * the copy. (Clients generally appreciate having things returned in the same |
| * order they were presented.) |
| * |
| * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is |
| * provided to create a linked hash map whose order of iteration is the order |
| * in which its entries were last accessed, from least-recently accessed to |
| * most-recently (<i>access-order</i>). This kind of map is well-suited to |
| * building LRU caches. Invoking the {@code put}, {@code putIfAbsent}, |
| * {@code get}, {@code getOrDefault}, {@code compute}, {@code computeIfAbsent}, |
| * {@code computeIfPresent}, or {@code merge} methods results |
| * in an access to the corresponding entry (assuming it exists after the |
| * invocation completes). The {@code replace} methods only result in an access |
| * of the entry if the value is replaced. The {@code putAll} method generates one |
| * entry access for each mapping in the specified map, in the order that |
| * key-value mappings are provided by the specified map's entry set iterator. |
| * <i>No other methods generate entry accesses.</i> In particular, operations |
| * on collection-views do <i>not</i> affect the order of iteration of the |
| * backing map. * |
| * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to |
| * impose a policy for removing stale mappings automatically when new mappings |
| * are added to the map. |
| * |
| * <p>This class provides all of the optional <tt>Map</tt> operations, and |
| * permits null elements. Like <tt>HashMap</tt>, it provides constant-time |
| * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and |
| * <tt>remove</tt>), assuming the hash function disperses elements |
| * properly among the buckets. Performance is likely to be just slightly |
| * below that of <tt>HashMap</tt>, due to the added expense of maintaining the |
| * linked list, with one exception: Iteration over the collection-views |
| * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i> |
| * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt> |
| * is likely to be more expensive, requiring time proportional to its |
| * <i>capacity</i>. |
| * |
| * <p>A linked hash map has two parameters that affect its performance: |
| * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely |
| * as for <tt>HashMap</tt>. Note, however, that the penalty for choosing an |
| * excessively high value for initial capacity is less severe for this class |
| * than for <tt>HashMap</tt>, as iteration times for this class are unaffected |
| * by capacity. |
| * |
| * <p><strong>Note that this implementation is not synchronized.</strong> |
| * If multiple threads access a linked hash map concurrently, and at least |
| * one of the threads modifies the map structurally, it <em>must</em> be |
| * synchronized externally. This is typically accomplished by |
| * synchronizing on some object that naturally encapsulates the map. |
| * |
| * If no such object exists, the map should be "wrapped" using the |
| * {@link Collections#synchronizedMap Collections.synchronizedMap} |
| * method. This is best done at creation time, to prevent accidental |
| * unsynchronized access to the map:<pre> |
| * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre> |
| * |
| * A structural modification is any operation that adds or deletes one or more |
| * mappings or, in the case of access-ordered linked hash maps, affects |
| * iteration order. In insertion-ordered linked hash maps, merely changing |
| * the value associated with a key that is already contained in the map is not |
| * a structural modification. <strong>In access-ordered linked hash maps, |
| * merely querying the map with <tt>get</tt> is a structural |
| * modification.</strong>) |
| * |
| * <p>The iterators returned by the <tt>iterator</tt> method of the collections |
| * returned by all of this class's collection view methods are |
| * <em>fail-fast</em>: if the map is structurally modified at any time after |
| * the iterator is created, in any way except through the iterator's own |
| * <tt>remove</tt> method, the iterator will throw 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>The spliterators returned by the spliterator method of the collections |
| * returned by all of this class's collection view methods are |
| * <em><a href="Spliterator.html#binding">late-binding</a></em>, |
| * <em>fail-fast</em>, and additionally report {@link Spliterator#ORDERED}. |
| * |
| * <p>This class is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @implNote |
| * The spliterators returned by the spliterator method of the collections |
| * returned by all of this class's collection view methods are created from |
| * the iterators of the corresponding collections. |
| * |
| * @param <K> the type of keys maintained by this map |
| * @param <V> the type of mapped values |
| * |
| * @author Josh Bloch |
| * @see Object#hashCode() |
| * @see Collection |
| * @see Map |
| * @see HashMap |
| * @see TreeMap |
| * @see Hashtable |
| * @since 1.4 |
| */ |
| |
| public class LinkedHashMap<K,V> |
| extends HashMap<K,V> |
| implements Map<K,V> |
| { |
| |
| private static final long serialVersionUID = 3801124242820219131L; |
| |
| /** |
| * The head of the doubly linked list. |
| */ |
| private transient LinkedHashMapEntry<K,V> header; |
| |
| /** |
| * The iteration ordering method for this linked hash map: <tt>true</tt> |
| * for access-order, <tt>false</tt> for insertion-order. |
| * |
| * @serial |
| */ |
| private final boolean accessOrder; |
| |
| /** |
| * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance |
| * with the specified initial capacity and load factor. |
| * |
| * @param initialCapacity the initial capacity |
| * @param loadFactor the load factor |
| * @throws IllegalArgumentException if the initial capacity is negative |
| * or the load factor is nonpositive |
| */ |
| public LinkedHashMap(int initialCapacity, float loadFactor) { |
| super(initialCapacity, loadFactor); |
| accessOrder = false; |
| } |
| |
| /** |
| * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance |
| * with the specified initial capacity and a default load factor (0.75). |
| * |
| * @param initialCapacity the initial capacity |
| * @throws IllegalArgumentException if the initial capacity is negative |
| */ |
| public LinkedHashMap(int initialCapacity) { |
| super(initialCapacity); |
| accessOrder = false; |
| } |
| |
| /** |
| * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance |
| * with the default initial capacity (16) and load factor (0.75). |
| */ |
| public LinkedHashMap() { |
| super(); |
| accessOrder = false; |
| } |
| |
| /** |
| * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with |
| * the same mappings as the specified map. The <tt>LinkedHashMap</tt> |
| * instance is created with a default load factor (0.75) and an initial |
| * capacity sufficient to hold the mappings in the specified map. |
| * |
| * @param m the map whose mappings are to be placed in this map |
| * @throws NullPointerException if the specified map is null |
| */ |
| public LinkedHashMap(Map<? extends K, ? extends V> m) { |
| super(m); |
| accessOrder = false; |
| } |
| |
| /** |
| * Constructs an empty <tt>LinkedHashMap</tt> instance with the |
| * specified initial capacity, load factor and ordering mode. |
| * |
| * @param initialCapacity the initial capacity |
| * @param loadFactor the load factor |
| * @param accessOrder the ordering mode - <tt>true</tt> for |
| * access-order, <tt>false</tt> for insertion-order |
| * @throws IllegalArgumentException if the initial capacity is negative |
| * or the load factor is nonpositive |
| */ |
| public LinkedHashMap(int initialCapacity, |
| float loadFactor, |
| boolean accessOrder) { |
| super(initialCapacity, loadFactor); |
| this.accessOrder = accessOrder; |
| } |
| |
| /** |
| * Called by superclass constructors and pseudoconstructors (clone, |
| * readObject) before any entries are inserted into the map. Initializes |
| * the chain. |
| */ |
| @Override |
| void init() { |
| header = new LinkedHashMapEntry<>(-1, null, null, null); |
| header.before = header.after = header; |
| } |
| |
| /** |
| * Transfers all entries to new table array. This method is called |
| * by superclass resize. It is overridden for performance, as it is |
| * faster to iterate using our linked list. |
| */ |
| @Override |
| void transfer(HashMapEntry[] newTable, boolean rehash) { |
| int newCapacity = newTable.length; |
| for (LinkedHashMapEntry<K,V> e = header.after; e != header; e = e.after) { |
| if (rehash) |
| e.hash = (e.key == null) ? 0 : hash(e.key); |
| int index = indexFor(e.hash, newCapacity); |
| e.next = newTable[index]; |
| newTable[index] = e; |
| } |
| } |
| |
| |
| /** |
| * Returns <tt>true</tt> if this map maps one or more keys to the |
| * specified value. |
| * |
| * @param value value whose presence in this map is to be tested |
| * @return <tt>true</tt> if this map maps one or more keys to the |
| * specified value |
| */ |
| public boolean containsValue(Object value) { |
| // Overridden to take advantage of faster iterator |
| if (value==null) { |
| for (LinkedHashMapEntry e = header.after; e != header; e = e.after) |
| if (e.value==null) |
| return true; |
| } else { |
| for (LinkedHashMapEntry e = header.after; e != header; e = e.after) |
| if (value.equals(e.value)) |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Returns the value to which the specified key is mapped, |
| * or {@code null} if this map contains no mapping for the key. |
| * |
| * <p>More formally, if this map contains a mapping from a key |
| * {@code k} to a value {@code v} such that {@code (key==null ? k==null : |
| * key.equals(k))}, then this method returns {@code v}; otherwise |
| * it returns {@code null}. (There can be at most one such mapping.) |
| * |
| * <p>A return value of {@code null} does not <i>necessarily</i> |
| * indicate that the map contains no mapping for the key; it's also |
| * possible that the map explicitly maps the key to {@code null}. |
| * The {@link #containsKey containsKey} operation may be used to |
| * distinguish these two cases. |
| */ |
| public V get(Object key) { |
| LinkedHashMapEntry<K,V> e = (LinkedHashMapEntry<K,V>)getEntry(key); |
| if (e == null) |
| return null; |
| e.recordAccess(this); |
| return e.value; |
| } |
| |
| /** |
| * Removes all of the mappings from this map. |
| * The map will be empty after this call returns. |
| */ |
| public void clear() { |
| super.clear(); |
| header.before = header.after = header; |
| } |
| |
| /** |
| * LinkedHashMap entry. |
| */ |
| private static class LinkedHashMapEntry<K,V> extends HashMapEntry<K,V> { |
| // These fields comprise the doubly linked list used for iteration. |
| LinkedHashMapEntry<K,V> before, after; |
| |
| LinkedHashMapEntry(int hash, K key, V value, HashMapEntry<K,V> next) { |
| super(hash, key, value, next); |
| } |
| |
| /** |
| * Removes this entry from the linked list. |
| */ |
| private void remove() { |
| before.after = after; |
| after.before = before; |
| } |
| |
| /** |
| * Inserts this entry before the specified existing entry in the list. |
| */ |
| private void addBefore(LinkedHashMapEntry<K,V> existingEntry) { |
| after = existingEntry; |
| before = existingEntry.before; |
| before.after = this; |
| after.before = this; |
| } |
| |
| /** |
| * This method is invoked by the superclass whenever the value |
| * of a pre-existing entry is read by Map.get or modified by Map.set. |
| * If the enclosing Map is access-ordered, it moves the entry |
| * to the end of the list; otherwise, it does nothing. |
| */ |
| void recordAccess(HashMap<K,V> m) { |
| LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m; |
| if (lm.accessOrder) { |
| lm.modCount++; |
| remove(); |
| addBefore(lm.header); |
| } |
| } |
| |
| void recordRemoval(HashMap<K,V> m) { |
| remove(); |
| } |
| } |
| |
| private abstract class LinkedHashIterator<T> implements Iterator<T> { |
| LinkedHashMapEntry<K,V> nextEntry = header.after; |
| LinkedHashMapEntry<K,V> lastReturned = null; |
| |
| /** |
| * The modCount value that the iterator believes that the backing |
| * List should have. If this expectation is violated, the iterator |
| * has detected concurrent modification. |
| */ |
| int expectedModCount = modCount; |
| |
| public boolean hasNext() { |
| return nextEntry != header; |
| } |
| |
| public void remove() { |
| if (lastReturned == null) |
| throw new IllegalStateException(); |
| if (modCount != expectedModCount) |
| throw new ConcurrentModificationException(); |
| |
| LinkedHashMap.this.remove(lastReturned.key); |
| lastReturned = null; |
| expectedModCount = modCount; |
| } |
| |
| Entry<K,V> nextEntry() { |
| if (modCount != expectedModCount) |
| throw new ConcurrentModificationException(); |
| if (nextEntry == header) |
| throw new NoSuchElementException(); |
| |
| LinkedHashMapEntry<K,V> e = lastReturned = nextEntry; |
| nextEntry = e.after; |
| return e; |
| } |
| } |
| |
| private class KeyIterator extends LinkedHashIterator<K> { |
| public K next() { return nextEntry().getKey(); } |
| } |
| |
| private class ValueIterator extends LinkedHashIterator<V> { |
| public V next() { return nextEntry().getValue(); } |
| } |
| |
| private class EntryIterator extends LinkedHashIterator<Map.Entry<K,V>> { |
| public Map.Entry<K,V> next() { return nextEntry(); } |
| } |
| |
| // These Overrides alter the behavior of superclass view iterator() methods |
| Iterator<K> newKeyIterator() { return new KeyIterator(); } |
| Iterator<V> newValueIterator() { return new ValueIterator(); } |
| Iterator<Map.Entry<K,V>> newEntryIterator() { return new EntryIterator(); } |
| |
| /** |
| * This override alters behavior of superclass put method. It causes newly |
| * allocated entry to get inserted at the end of the linked list and |
| * removes the eldest entry if appropriate. |
| */ |
| void addEntry(int hash, K key, V value, int bucketIndex) { |
| super.addEntry(hash, key, value, bucketIndex); |
| |
| // Remove eldest entry if instructed |
| LinkedHashMapEntry<K,V> eldest = header.after; |
| if (removeEldestEntry(eldest)) { |
| removeEntryForKey(eldest.key); |
| } |
| } |
| |
| /** |
| * Returns the eldest entry in the map, or {@code null} if the map is empty. |
| * |
| * Android-added. |
| * |
| * @hide |
| */ |
| public Map.Entry<K, V> eldest() { |
| Entry<K, V> eldest = header.after; |
| return eldest != header ? eldest : null; |
| } |
| |
| /** |
| * This override differs from addEntry in that it doesn't resize the |
| * table or remove the eldest entry. |
| */ |
| void createEntry(int hash, K key, V value, int bucketIndex) { |
| HashMapEntry<K,V> old = table[bucketIndex]; |
| LinkedHashMapEntry<K,V> e = new LinkedHashMapEntry<>(hash, key, value, old); |
| table[bucketIndex] = e; |
| e.addBefore(header); |
| size++; |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this map should remove its eldest entry. |
| * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after |
| * inserting a new entry into the map. It provides the implementor |
| * with the opportunity to remove the eldest entry each time a new one |
| * is added. This is useful if the map represents a cache: it allows |
| * the map to reduce memory consumption by deleting stale entries. |
| * |
| * <p>Sample use: this override will allow the map to grow up to 100 |
| * entries and then delete the eldest entry each time a new entry is |
| * added, maintaining a steady state of 100 entries. |
| * <pre> |
| * private static final int MAX_ENTRIES = 100; |
| * |
| * protected boolean removeEldestEntry(Map.Entry eldest) { |
| * return size() > MAX_ENTRIES; |
| * } |
| * </pre> |
| * |
| * <p>This method typically does not modify the map in any way, |
| * instead allowing the map to modify itself as directed by its |
| * return value. It <i>is</i> permitted for this method to modify |
| * the map directly, but if it does so, it <i>must</i> return |
| * <tt>false</tt> (indicating that the map should not attempt any |
| * further modification). The effects of returning <tt>true</tt> |
| * after modifying the map from within this method are unspecified. |
| * |
| * <p>This implementation merely returns <tt>false</tt> (so that this |
| * map acts like a normal map - the eldest element is never removed). |
| * |
| * @param eldest The least recently inserted entry in the map, or if |
| * this is an access-ordered map, the least recently accessed |
| * entry. This is the entry that will be removed it this |
| * method returns <tt>true</tt>. If the map was empty prior |
| * to the <tt>put</tt> or <tt>putAll</tt> invocation resulting |
| * in this invocation, this will be the entry that was just |
| * inserted; in other words, if the map contains a single |
| * entry, the eldest entry is also the newest. |
| * @return <tt>true</tt> if the eldest entry should be removed |
| * from the map; <tt>false</tt> if it should be retained. |
| */ |
| protected boolean removeEldestEntry(Map.Entry<K,V> eldest) { |
| return false; |
| } |
| |
| // Map overrides |
| public void forEach(BiConsumer<? super K, ? super V> action) { |
| if (action == null) |
| throw new NullPointerException(); |
| int mc = modCount; |
| // Android modified - breaks from the loop when modCount != mc |
| for (LinkedHashMapEntry<K,V> e = header.after; modCount == mc && e != header; e = e.after) |
| action.accept(e.key, e.value); |
| if (modCount != mc) |
| throw new ConcurrentModificationException(); |
| } |
| } |