/* * Copyright (c) 1998, 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.lang.ref.WeakReference; import java.lang.ref.ReferenceQueue; /** * Hash table based implementation of the Map interface, with * weak keys. * An entry in a WeakHashMap will automatically be removed when * its key is no longer in ordinary use. More precisely, the presence of a * mapping for a given key will not prevent the key from being discarded by the * garbage collector, that is, made finalizable, finalized, and then reclaimed. * When a key has been discarded its entry is effectively removed from the map, * so this class behaves somewhat differently from other Map * implementations. * *

Both null values and the null key are supported. This class has * performance characteristics similar to those of the HashMap * class, and has the same efficiency parameters of initial capacity * and load factor. * *

Like most collection classes, this class is not synchronized. * A synchronized WeakHashMap may be constructed using the * {@link Collections#synchronizedMap Collections.synchronizedMap} * method. * *

This class is intended primarily for use with key objects whose * equals methods test for object identity using the * == operator. Once such a key is discarded it can never be * recreated, so it is impossible to do a lookup of that key in a * WeakHashMap at some later time and be surprised that its entry * has been removed. This class will work perfectly well with key objects * whose equals methods are not based upon object identity, such * as String instances. With such recreatable key objects, * however, the automatic removal of WeakHashMap entries whose * keys have been discarded may prove to be confusing. * *

The behavior of the WeakHashMap class depends in part upon * the actions of the garbage collector, so several familiar (though not * required) Map invariants do not hold for this class. Because * the garbage collector may discard keys at any time, a * WeakHashMap may behave as though an unknown thread is silently * removing entries. In particular, even if you synchronize on a * WeakHashMap instance and invoke none of its mutator methods, it * is possible for the size method to return smaller values over * time, for the isEmpty method to return false and * then true, for the containsKey method to return * true and later false for a given key, for the * get method to return a value for a given key but later return * null, for the put method to return * null and the remove method to return * false for a key that previously appeared to be in the map, and * for successive examinations of the key set, the value collection, and * the entry set to yield successively smaller numbers of elements. * *

Each key object in a WeakHashMap is stored indirectly as * the referent of a weak reference. Therefore a key will automatically be * removed only after the weak references to it, both inside and outside of the * map, have been cleared by the garbage collector. * *

Implementation note: The value objects in a * WeakHashMap are held by ordinary strong references. Thus care * should be taken to ensure that value objects do not strongly refer to their * own keys, either directly or indirectly, since that will prevent the keys * from being discarded. Note that a value object may refer indirectly to its * key via the WeakHashMap itself; that is, a value object may * strongly refer to some other key object whose associated value object, in * turn, strongly refers to the key of the first value object. If the values * in the map do not rely on the map holding strong references to them, one way * to deal with this is to wrap values themselves within * WeakReferences before * inserting, as in: m.put(key, new WeakReference(value)), * and then unwrapping upon each get. * *

The iterators returned by the iterator method of the collections * returned by all of this class's "collection view methods" are * fail-fast: if the map is structurally modified at any time after the * iterator is created, in any way except through the iterator's own * remove 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. * *

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 ConcurrentModificationException on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: the fail-fast behavior of iterators * should be used only to detect bugs. * *

This class is a member of the * * Java Collections Framework. * * @param the type of keys maintained by this map * @param the type of mapped values * * @author Doug Lea * @author Josh Bloch * @author Mark Reinhold * @since 1.2 * @see java.util.HashMap * @see java.lang.ref.WeakReference */ public class WeakHashMap extends AbstractMap implements Map { /** * The default initial capacity -- MUST be a power of two. */ private static final int DEFAULT_INITIAL_CAPACITY = 16; /** * The maximum capacity, used if a higher value is implicitly specified * by either of the constructors with arguments. * MUST be a power of two <= 1<<30. */ private static final int MAXIMUM_CAPACITY = 1 << 30; /** * The load factor used when none specified in constructor. */ private static final float DEFAULT_LOAD_FACTOR = 0.75f; /** * The table, resized as necessary. Length MUST Always be a power of two. */ Entry[] table; /** * The number of key-value mappings contained in this weak hash map. */ private int size; /** * The next size value at which to resize (capacity * load factor). */ private int threshold; /** * The load factor for the hash table. */ private final float loadFactor; /** * Reference queue for cleared WeakEntries */ private final ReferenceQueue queue = new ReferenceQueue<>(); /** * The number of times this WeakHashMap has been structurally modified. * Structural modifications are those that change the number of * mappings in the map or otherwise modify its internal structure * (e.g., rehash). This field is used to make iterators on * Collection-views of the map fail-fast. * * @see ConcurrentModificationException */ int modCount; /** * The default threshold of map capacity above which alternative hashing is * used for String keys. Alternative hashing reduces the incidence of * collisions due to weak hash code calculation for String keys. *

* This value may be overridden by defining the system property * {@code jdk.map.althashing.threshold}. A property value of {@code 1} * forces alternative hashing to be used at all times whereas * {@code -1} value ensures that alternative hashing is never used. */ static final int ALTERNATIVE_HASHING_THRESHOLD_DEFAULT = Integer.MAX_VALUE; /** * holds values which can't be initialized until after VM is booted. */ private static class Holder { /** * Table capacity above which to switch to use alternative hashing. */ static final int ALTERNATIVE_HASHING_THRESHOLD; static { String altThreshold = java.security.AccessController.doPrivileged( new sun.security.action.GetPropertyAction( "jdk.map.althashing.threshold")); int threshold; try { threshold = (null != altThreshold) ? Integer.parseInt(altThreshold) : ALTERNATIVE_HASHING_THRESHOLD_DEFAULT; // disable alternative hashing if -1 if (threshold == -1) { threshold = Integer.MAX_VALUE; } if (threshold < 0) { throw new IllegalArgumentException("value must be positive integer."); } } catch(IllegalArgumentException failed) { throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed); } ALTERNATIVE_HASHING_THRESHOLD = threshold; } } /** * If {@code true} then perform alternate hashing to reduce the incidence of * collisions due to weak hash code calculation. */ transient boolean useAltHashing; /** * A randomizing value associated with this instance that is applied to * hash code of keys to make hash collisions harder to find. */ transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this); @SuppressWarnings("unchecked") private Entry[] newTable(int n) { return (Entry[]) new Entry[n]; } /** * Constructs a new, empty WeakHashMap with the given initial * capacity and the given load factor. * * @param initialCapacity The initial capacity of the WeakHashMap * @param loadFactor The load factor of the WeakHashMap * @throws IllegalArgumentException if the initial capacity is negative, * or if the load factor is nonpositive. */ public WeakHashMap(int initialCapacity, float loadFactor) { if (initialCapacity < 0) throw new IllegalArgumentException("Illegal Initial Capacity: "+ initialCapacity); if (initialCapacity > MAXIMUM_CAPACITY) initialCapacity = MAXIMUM_CAPACITY; if (loadFactor <= 0 || Float.isNaN(loadFactor)) throw new IllegalArgumentException("Illegal Load factor: "+ loadFactor); int capacity = 1; while (capacity < initialCapacity) capacity <<= 1; table = newTable(capacity); this.loadFactor = loadFactor; threshold = (int)(capacity * loadFactor); useAltHashing = sun.misc.VM.isBooted() && (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD); } /** * Constructs a new, empty WeakHashMap with the given initial * capacity and the default load factor (0.75). * * @param initialCapacity The initial capacity of the WeakHashMap * @throws IllegalArgumentException if the initial capacity is negative */ public WeakHashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); } /** * Constructs a new, empty WeakHashMap with the default initial * capacity (16) and load factor (0.75). */ public WeakHashMap() { this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); } /** * Constructs a new WeakHashMap with the same mappings as the * specified map. The WeakHashMap is created with the 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 * @since 1.3 */ public WeakHashMap(Map m) { this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR); putAll(m); } // internal utilities /** * Value representing null keys inside tables. */ private static final Object NULL_KEY = new Object(); /** * Use NULL_KEY for key if it is null. */ private static Object maskNull(Object key) { return (key == null) ? NULL_KEY : key; } /** * Returns internal representation of null key back to caller as null. */ static Object unmaskNull(Object key) { return (key == NULL_KEY) ? null : key; } /** * Checks for equality of non-null reference x and possibly-null y. By * default uses Object.equals. */ private static boolean eq(Object x, Object y) { return x == y || x.equals(y); } /** * Retrieve object hash code and applies a supplemental hash function to the * result hash, which defends against poor quality hash functions. This is * critical because HashMap uses power-of-two length hash tables, that * otherwise encounter collisions for hashCodes that do not differ * in lower bits. */ int hash(Object k) { int h; if (useAltHashing) { h = hashSeed; if (k instanceof String) { return sun.misc.Hashing.stringHash32((String) k); } else { h ^= k.hashCode(); } } else { h = k.hashCode(); } // This function ensures that hashCodes that differ only by // constant multiples at each bit position have a bounded // number of collisions (approximately 8 at default load factor). h ^= (h >>> 20) ^ (h >>> 12); return h ^ (h >>> 7) ^ (h >>> 4); } /** * Returns index for hash code h. */ private static int indexFor(int h, int length) { return h & (length-1); } /** * Expunges stale entries from the table. */ private void expungeStaleEntries() { for (Object x; (x = queue.poll()) != null; ) { synchronized (queue) { @SuppressWarnings("unchecked") Entry e = (Entry) x; int i = indexFor(e.hash, table.length); Entry prev = table[i]; Entry p = prev; while (p != null) { Entry next = p.next; if (p == e) { if (prev == e) table[i] = next; else prev.next = next; // Must not null out e.next; // stale entries may be in use by a HashIterator e.value = null; // Help GC size--; break; } prev = p; p = next; } } } } /** * Returns the table after first expunging stale entries. */ private Entry[] getTable() { expungeStaleEntries(); return table; } /** * Returns the number of key-value mappings in this map. * This result is a snapshot, and may not reflect unprocessed * entries that will be removed before next attempted access * because they are no longer referenced. */ public int size() { if (size == 0) return 0; expungeStaleEntries(); return size; } /** * Returns true if this map contains no key-value mappings. * This result is a snapshot, and may not reflect unprocessed * entries that will be removed before next attempted access * because they are no longer referenced. */ public boolean isEmpty() { return size() == 0; } /** * Returns the value to which the specified key is mapped, * or {@code null} if this map contains no mapping for the key. * *

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.) * *

A return value of {@code null} does not necessarily * 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. * * @see #put(Object, Object) */ public V get(Object key) { Object k = maskNull(key); int h = hash(k); Entry[] tab = getTable(); int index = indexFor(h, tab.length); Entry e = tab[index]; while (e != null) { if (e.hash == h && eq(k, e.get())) return e.value; e = e.next; } return null; } /** * Returns true if this map contains a mapping for the * specified key. * * @param key The key whose presence in this map is to be tested * @return true if there is a mapping for key; * false otherwise */ public boolean containsKey(Object key) { return getEntry(key) != null; } /** * Returns the entry associated with the specified key in this map. * Returns null if the map contains no mapping for this key. */ Entry getEntry(Object key) { Object k = maskNull(key); int h = hash(k); Entry[] tab = getTable(); int index = indexFor(h, tab.length); Entry e = tab[index]; while (e != null && !(e.hash == h && eq(k, e.get()))) e = e.next; return e; } /** * Associates the specified value with the specified key in this map. * If the map previously contained a mapping for this key, the old * value is replaced. * * @param key key with which the specified value is to be associated. * @param value value to be associated with the specified key. * @return the previous value associated with key, or * null if there was no mapping for key. * (A null return can also indicate that the map * previously associated null with key.) */ public V put(K key, V value) { Object k = maskNull(key); int h = hash(k); Entry[] tab = getTable(); int i = indexFor(h, tab.length); for (Entry e = tab[i]; e != null; e = e.next) { if (h == e.hash && eq(k, e.get())) { V oldValue = e.value; if (value != oldValue) e.value = value; return oldValue; } } modCount++; Entry e = tab[i]; tab[i] = new Entry<>(k, value, queue, h, e); if (++size >= threshold) resize(tab.length * 2); return null; } /** * Rehashes the contents of this map into a new array with a * larger capacity. This method is called automatically when the * number of keys in this map reaches its threshold. * * If current capacity is MAXIMUM_CAPACITY, this method does not * resize the map, but sets threshold to Integer.MAX_VALUE. * This has the effect of preventing future calls. * * @param newCapacity the new capacity, MUST be a power of two; * must be greater than current capacity unless current * capacity is MAXIMUM_CAPACITY (in which case value * is irrelevant). */ void resize(int newCapacity) { Entry[] oldTable = getTable(); int oldCapacity = oldTable.length; if (oldCapacity == MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return; } Entry[] newTable = newTable(newCapacity); boolean oldAltHashing = useAltHashing; useAltHashing |= sun.misc.VM.isBooted() && (newCapacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD); boolean rehash = oldAltHashing ^ useAltHashing; transfer(oldTable, newTable, rehash); table = newTable; /* * If ignoring null elements and processing ref queue caused massive * shrinkage, then restore old table. This should be rare, but avoids * unbounded expansion of garbage-filled tables. */ if (size >= threshold / 2) { threshold = (int)(newCapacity * loadFactor); } else { expungeStaleEntries(); transfer(newTable, oldTable, false); table = oldTable; } } /** Transfers all entries from src to dest tables */ private void transfer(Entry[] src, Entry[] dest, boolean rehash) { for (int j = 0; j < src.length; ++j) { Entry e = src[j]; src[j] = null; while (e != null) { Entry next = e.next; Object key = e.get(); if (key == null) { e.next = null; // Help GC e.value = null; // " " size--; } else { if (rehash) { e.hash = hash(key); } int i = indexFor(e.hash, dest.length); e.next = dest[i]; dest[i] = e; } e = next; } } } /** * Copies all of the mappings from the specified map to this map. * These mappings will replace any mappings that this map had for any * of the keys currently in the specified map. * * @param m mappings to be stored in this map. * @throws NullPointerException if the specified map is null. */ public void putAll(Map m) { int numKeysToBeAdded = m.size(); if (numKeysToBeAdded == 0) return; /* * Expand the map if the map if the number of mappings to be added * is greater than or equal to threshold. This is conservative; the * obvious condition is (m.size() + size) >= threshold, but this * condition could result in a map with twice the appropriate capacity, * if the keys to be added overlap with the keys already in this map. * By using the conservative calculation, we subject ourself * to at most one extra resize. */ if (numKeysToBeAdded > threshold) { int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); if (targetCapacity > MAXIMUM_CAPACITY) targetCapacity = MAXIMUM_CAPACITY; int newCapacity = table.length; while (newCapacity < targetCapacity) newCapacity <<= 1; if (newCapacity > table.length) resize(newCapacity); } for (Map.Entry e : m.entrySet()) put(e.getKey(), e.getValue()); } /** * Removes the mapping for a key from this weak hash map if it is present. * More formally, if this map contains a mapping from key k to * value v such that (key==null ? k==null : * key.equals(k)), that mapping is removed. (The map can contain * at most one such mapping.) * *

Returns the value to which this map previously associated the key, * or null if the map contained no mapping for the key. A * return value of null does not necessarily indicate * that the map contained no mapping for the key; it's also possible * that the map explicitly mapped the key to null. * *

The map will not contain a mapping for the specified key once the * call returns. * * @param key key whose mapping is to be removed from the map * @return the previous value associated with key, or * null if there was no mapping for key */ public V remove(Object key) { Object k = maskNull(key); int h = hash(k); Entry[] tab = getTable(); int i = indexFor(h, tab.length); Entry prev = tab[i]; Entry e = prev; while (e != null) { Entry next = e.next; if (h == e.hash && eq(k, e.get())) { modCount++; size--; if (prev == e) tab[i] = next; else prev.next = next; return e.value; } prev = e; e = next; } return null; } /** Special version of remove needed by Entry set */ boolean removeMapping(Object o) { if (!(o instanceof Map.Entry)) return false; Entry[] tab = getTable(); Map.Entry entry = (Map.Entry)o; Object k = maskNull(entry.getKey()); int h = hash(k); int i = indexFor(h, tab.length); Entry prev = tab[i]; Entry e = prev; while (e != null) { Entry next = e.next; if (h == e.hash && e.equals(entry)) { modCount++; size--; if (prev == e) tab[i] = next; else prev.next = next; return true; } prev = e; e = next; } return false; } /** * Removes all of the mappings from this map. * The map will be empty after this call returns. */ public void clear() { // clear out ref queue. We don't need to expunge entries // since table is getting cleared. while (queue.poll() != null) ; modCount++; Arrays.fill(table, null); size = 0; // Allocation of array may have caused GC, which may have caused // additional entries to go stale. Removing these entries from the // reference queue will make them eligible for reclamation. while (queue.poll() != null) ; } /** * Returns true 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 true if this map maps one or more keys to the * specified value */ public boolean containsValue(Object value) { if (value==null) return containsNullValue(); Entry[] tab = getTable(); for (int i = tab.length; i-- > 0;) for (Entry e = tab[i]; e != null; e = e.next) if (value.equals(e.value)) return true; return false; } /** * Special-case code for containsValue with null argument */ private boolean containsNullValue() { Entry[] tab = getTable(); for (int i = tab.length; i-- > 0;) for (Entry e = tab[i]; e != null; e = e.next) if (e.value==null) return true; return false; } /** * The entries in this hash table extend WeakReference, using its main ref * field as the key. */ private static class Entry extends WeakReference implements Map.Entry { V value; int hash; Entry next; /** * Creates new entry. */ Entry(Object key, V value, ReferenceQueue queue, int hash, Entry next) { super(key, queue); this.value = value; this.hash = hash; this.next = next; } @SuppressWarnings("unchecked") public K getKey() { return (K) WeakHashMap.unmaskNull(get()); } public V getValue() { return value; } public V setValue(V newValue) { V oldValue = value; value = newValue; return oldValue; } public boolean equals(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry e = (Map.Entry)o; K k1 = getKey(); Object k2 = e.getKey(); if (k1 == k2 || (k1 != null && k1.equals(k2))) { V v1 = getValue(); Object v2 = e.getValue(); if (v1 == v2 || (v1 != null && v1.equals(v2))) return true; } return false; } public int hashCode() { K k = getKey(); V v = getValue(); return ((k==null ? 0 : k.hashCode()) ^ (v==null ? 0 : v.hashCode())); } public String toString() { return getKey() + "=" + getValue(); } } private abstract class HashIterator implements Iterator { private int index; private Entry entry = null; private Entry lastReturned = null; private int expectedModCount = modCount; /** * Strong reference needed to avoid disappearance of key * between hasNext and next */ private Object nextKey = null; /** * Strong reference needed to avoid disappearance of key * between nextEntry() and any use of the entry */ private Object currentKey = null; HashIterator() { index = isEmpty() ? 0 : table.length; } public boolean hasNext() { Entry[] t = table; while (nextKey == null) { Entry e = entry; int i = index; while (e == null && i > 0) e = t[--i]; entry = e; index = i; if (e == null) { currentKey = null; return false; } nextKey = e.get(); // hold on to key in strong ref if (nextKey == null) entry = entry.next; } return true; } /** The common parts of next() across different types of iterators */ protected Entry nextEntry() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); if (nextKey == null && !hasNext()) throw new NoSuchElementException(); lastReturned = entry; entry = entry.next; currentKey = nextKey; nextKey = null; return lastReturned; } public void remove() { if (lastReturned == null) throw new IllegalStateException(); if (modCount != expectedModCount) throw new ConcurrentModificationException(); WeakHashMap.this.remove(currentKey); expectedModCount = modCount; lastReturned = null; currentKey = null; } } private class ValueIterator extends HashIterator { public V next() { return nextEntry().value; } } private class KeyIterator extends HashIterator { public K next() { return nextEntry().getKey(); } } private class EntryIterator extends HashIterator> { public Map.Entry next() { return nextEntry(); } } // Views private transient Set> entrySet = null; /** * Returns a {@link Set} view of the keys contained in this map. * The set is backed by the map, so changes to the map are * reflected in the set, and vice-versa. If the map is modified * while an iteration over the set is in progress (except through * the iterator's own remove operation), the results of * the iteration are undefined. The set supports element removal, * which removes the corresponding mapping from the map, via the * Iterator.remove, Set.remove, * removeAll, retainAll, and clear * operations. It does not support the add or addAll * operations. */ public Set keySet() { Set ks = keySet; return (ks != null ? ks : (keySet = new KeySet())); } private class KeySet extends AbstractSet { public Iterator iterator() { return new KeyIterator(); } public int size() { return WeakHashMap.this.size(); } public boolean contains(Object o) { return containsKey(o); } public boolean remove(Object o) { if (containsKey(o)) { WeakHashMap.this.remove(o); return true; } else return false; } public void clear() { WeakHashMap.this.clear(); } } /** * Returns a {@link Collection} view of the values contained in this map. * The collection is backed by the map, so changes to the map are * reflected in the collection, and vice-versa. If the map is * modified while an iteration over the collection is in progress * (except through the iterator's own remove operation), * the results of the iteration are undefined. The collection * supports element removal, which removes the corresponding * mapping from the map, via the Iterator.remove, * Collection.remove, removeAll, * retainAll and clear operations. It does not * support the add or addAll operations. */ public Collection values() { Collection vs = values; return (vs != null) ? vs : (values = new Values()); } private class Values extends AbstractCollection { public Iterator iterator() { return new ValueIterator(); } public int size() { return WeakHashMap.this.size(); } public boolean contains(Object o) { return containsValue(o); } public void clear() { WeakHashMap.this.clear(); } } /** * Returns a {@link Set} view of the mappings contained in this map. * The set is backed by the map, so changes to the map are * reflected in the set, and vice-versa. If the map is modified * while an iteration over the set is in progress (except through * the iterator's own remove operation, or through the * setValue operation on a map entry returned by the * iterator) the results of the iteration are undefined. The set * supports element removal, which removes the corresponding * mapping from the map, via the Iterator.remove, * Set.remove, removeAll, retainAll and * clear operations. It does not support the * add or addAll operations. */ public Set> entrySet() { Set> es = entrySet; return es != null ? es : (entrySet = new EntrySet()); } private class EntrySet extends AbstractSet> { public Iterator> iterator() { return new EntryIterator(); } public boolean contains(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry e = (Map.Entry)o; Entry candidate = getEntry(e.getKey()); return candidate != null && candidate.equals(e); } public boolean remove(Object o) { return removeMapping(o); } public int size() { return WeakHashMap.this.size(); } public void clear() { WeakHashMap.this.clear(); } private List> deepCopy() { List> list = new ArrayList<>(size()); for (Map.Entry e : this) list.add(new AbstractMap.SimpleEntry<>(e)); return list; } public Object[] toArray() { return deepCopy().toArray(); } public T[] toArray(T[] a) { return deepCopy().toArray(a); } } }