Java tutorial
/* * Copyright (c) 1998, 2018, 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; import java.util.concurrent.ThreadLocalRandom; import java.util.function.BiConsumer; import java.util.function.BiFunction; import java.util.function.Consumer; /** * Hash table based implementation of the {@code Map} interface, with * <em>weak keys</em>. * An entry in a {@code 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 {@code Map} * implementations. * * <p> Both null values and the null key are supported. This class has * performance characteristics similar to those of the {@code HashMap} * class, and has the same efficiency parameters of <em>initial capacity</em> * and <em>load factor</em>. * * <p> Like most collection classes, this class is not synchronized. * A synchronized {@code WeakHashMap} may be constructed using the * {@link Collections#synchronizedMap Collections.synchronizedMap} * method. * * <p> This class is intended primarily for use with key objects whose * {@code equals} methods test for object identity using the * {@code ==} 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 * {@code WeakHashMap} at some later time and be surprised that its entry * has been removed. This class will work perfectly well with key objects * whose {@code equals} methods are not based upon object identity, such * as {@code String} instances. With such recreatable key objects, * however, the automatic removal of {@code WeakHashMap} entries whose * keys have been discarded may prove to be confusing. * * <p> The behavior of the {@code WeakHashMap} class depends in part upon * the actions of the garbage collector, so several familiar (though not * required) {@code Map} invariants do not hold for this class. Because * the garbage collector may discard keys at any time, a * {@code WeakHashMap} may behave as though an unknown thread is silently * removing entries. In particular, even if you synchronize on a * {@code WeakHashMap} instance and invoke none of its mutator methods, it * is possible for the {@code size} method to return smaller values over * time, for the {@code isEmpty} method to return {@code false} and * then {@code true}, for the {@code containsKey} method to return * {@code true} and later {@code false} for a given key, for the * {@code get} method to return a value for a given key but later return * {@code null}, for the {@code put} method to return * {@code null} and the {@code remove} method to return * {@code 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. * * <p> Each key object in a {@code 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. * * <p> <strong>Implementation note:</strong> The value objects in a * {@code 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 {@code 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 * {@code WeakReferences} before * inserting, as in: {@code m.put(key, new WeakReference(value))}, * and then unwrapping upon each {@code get}. * * <p>The iterators returned by the {@code iterator} method of the collections * returned by all of this class's "collection view methods" are * <i>fail-fast</i>: if the map is structurally modified at any time after the * iterator is created, in any way except through the iterator's own * {@code 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. * * <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 {@code ConcurrentModificationException} 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}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @param <K> the type of keys maintained by this map * @param <V> 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<K, V> extends AbstractMap<K, V> implements Map<K, V> { /** * 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<K, V>[] 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<Object> 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; @SuppressWarnings("unchecked") private Entry<K, V>[] newTable(int n) { return (Entry<K, V>[]) new Entry<?, ?>[n]; } /** * Constructs a new, empty {@code WeakHashMap} with the given initial * capacity and the given load factor. * * @param initialCapacity The initial capacity of the {@code WeakHashMap} * @param loadFactor The load factor of the {@code 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); } /** * Constructs a new, empty {@code WeakHashMap} with the given initial * capacity and the default load factor (0.75). * * @param initialCapacity The initial capacity of the {@code WeakHashMap} * @throws IllegalArgumentException if the initial capacity is negative */ public WeakHashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); } /** * Constructs a new, empty {@code WeakHashMap} with the default initial * capacity (16) and load factor (0.75). */ public WeakHashMap() { this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); } /** * Constructs a new {@code WeakHashMap} with the same mappings as the * specified map. The {@code 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<? extends K, ? extends V> m) { this(Math.max((int) ((float) m.size() / DEFAULT_LOAD_FACTOR + 1.0F), 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. */ final int hash(Object k) { int 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<K, V> e = (Entry<K, V>) x; int i = indexFor(e.hash, table.length); Entry<K, V> prev = table[i]; Entry<K, V> p = prev; while (p != null) { Entry<K, V> 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<K, V>[] 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 {@code 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. * * <p>More formally, if this map contains a mapping from a key * {@code k} to a value {@code v} such that * {@code Objects.equals(key, 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. * * @see #put(Object, Object) */ public V get(Object key) { Object k = maskNull(key); int h = hash(k); Entry<K, V>[] tab = getTable(); int index = indexFor(h, tab.length); Entry<K, V> e = tab[index]; while (e != null) { if (e.hash == h && eq(k, e.get())) return e.value; e = e.next; } return null; } /** * Returns {@code 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 {@code true} if there is a mapping for {@code key}; * {@code 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<K, V> getEntry(Object key) { Object k = maskNull(key); int h = hash(k); Entry<K, V>[] tab = getTable(); int index = indexFor(h, tab.length); Entry<K, V> 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 {@code key}, or * {@code null} if there was no mapping for {@code key}. * (A {@code null} return can also indicate that the map * previously associated {@code null} with {@code key}.) */ public V put(K key, V value) { Object k = maskNull(key); int h = hash(k); Entry<K, V>[] tab = getTable(); int i = indexFor(h, tab.length); for (Entry<K, V> 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<K, V> 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<K, V>[] oldTable = getTable(); int oldCapacity = oldTable.length; if (oldCapacity == MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return; } Entry<K, V>[] newTable = newTable(newCapacity); transfer(oldTable, newTable); 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); table = oldTable; } } /** Transfers all entries from src to dest tables */ private void transfer(Entry<K, V>[] src, Entry<K, V>[] dest) { for (int j = 0; j < src.length; ++j) { Entry<K, V> e = src[j]; src[j] = null; while (e != null) { Entry<K, V> next = e.next; Object key = e.get(); if (key == null) { e.next = null; // Help GC e.value = null; // " " size--; } else { 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<? extends K, ? extends V> 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<? extends K, ? extends V> 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 {@code k} to * value {@code v} such that <code>(key==null ? k==null : * key.equals(k))</code>, that mapping is removed. (The map can contain * at most one such mapping.) * * <p>Returns the value to which this map previously associated the key, * or {@code null} if the map contained no mapping for the key. A * return value of {@code null} does not <i>necessarily</i> indicate * that the map contained no mapping for the key; it's also possible * that the map explicitly mapped the key to {@code null}. * * <p>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 {@code key}, or * {@code null} if there was no mapping for {@code key} */ public V remove(Object key) { Object k = maskNull(key); int h = hash(k); Entry<K, V>[] tab = getTable(); int i = indexFor(h, tab.length); Entry<K, V> prev = tab[i]; Entry<K, V> e = prev; while (e != null) { Entry<K, V> 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<K, V>[] tab = getTable(); Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o; Object k = maskNull(entry.getKey()); int h = hash(k); int i = indexFor(h, tab.length); Entry<K, V> prev = tab[i]; Entry<K, V> e = prev; while (e != null) { Entry<K, V> 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 {@code 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 {@code true} if this map maps one or more keys to the * specified value */ public boolean containsValue(Object value) { if (value == null) return containsNullValue(); Entry<K, V>[] tab = getTable(); for (int i = tab.length; i-- > 0;) for (Entry<K, V> 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<K, V>[] tab = getTable(); for (int i = tab.length; i-- > 0;) for (Entry<K, V> 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<K, V> extends WeakReference<Object> implements Map.Entry<K, V> { V value; final int hash; Entry<K, V> next; /** * Creates new entry. */ Entry(Object key, V value, ReferenceQueue<Object> queue, int hash, Entry<K, V> 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 Objects.hashCode(k) ^ Objects.hashCode(v); } public String toString() { return getKey() + "=" + getValue(); } } private abstract class HashIterator<T> implements Iterator<T> { private int index; private Entry<K, V> entry; private Entry<K, V> lastReturned; private int expectedModCount = modCount; /** * Strong reference needed to avoid disappearance of key * between hasNext and next */ private Object nextKey; /** * Strong reference needed to avoid disappearance of key * between nextEntry() and any use of the entry */ private Object currentKey; HashIterator() { index = isEmpty() ? 0 : table.length; } public boolean hasNext() { Entry<K, V>[] t = table; while (nextKey == null) { Entry<K, V> 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<K, V> 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<V> { public V next() { return nextEntry().value; } } private class KeyIterator extends HashIterator<K> { public K next() { return nextEntry().getKey(); } } private class EntryIterator extends HashIterator<Map.Entry<K, V>> { public Map.Entry<K, V> next() { return nextEntry(); } } // Views private transient Set<Map.Entry<K, V>> entrySet; /** * 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 {@code remove} operation), the results of * the iteration are undefined. The set supports element removal, * which removes the corresponding mapping from the map, via the * {@code Iterator.remove}, {@code Set.remove}, * {@code removeAll}, {@code retainAll}, and {@code clear} * operations. It does not support the {@code add} or {@code addAll} * operations. */ public Set<K> keySet() { Set<K> ks = keySet; if (ks == null) { ks = new KeySet(); keySet = ks; } return ks; } private class KeySet extends AbstractSet<K> { public Iterator<K> 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(); } public Spliterator<K> spliterator() { return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); } } /** * 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 {@code remove} operation), * the results of the iteration are undefined. The collection * supports element removal, which removes the corresponding * mapping from the map, via the {@code Iterator.remove}, * {@code Collection.remove}, {@code removeAll}, * {@code retainAll} and {@code clear} operations. It does not * support the {@code add} or {@code addAll} operations. */ public Collection<V> values() { Collection<V> vs = values; if (vs == null) { vs = new Values(); values = vs; } return vs; } private class Values extends AbstractCollection<V> { public Iterator<V> 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(); } public Spliterator<V> spliterator() { return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0); } } /** * 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 {@code remove} operation, or through the * {@code 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 {@code Iterator.remove}, * {@code Set.remove}, {@code removeAll}, {@code retainAll} and * {@code clear} operations. It does not support the * {@code add} or {@code addAll} operations. */ public Set<Map.Entry<K, V>> entrySet() { Set<Map.Entry<K, V>> es = entrySet; return es != null ? es : (entrySet = new EntrySet()); } private class EntrySet extends AbstractSet<Map.Entry<K, V>> { public Iterator<Map.Entry<K, V>> iterator() { return new EntryIterator(); } public boolean contains(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; Entry<K, V> 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<Map.Entry<K, V>> deepCopy() { List<Map.Entry<K, V>> list = new ArrayList<>(size()); for (Map.Entry<K, V> e : this) list.add(new AbstractMap.SimpleEntry<>(e)); return list; } public Object[] toArray() { return deepCopy().toArray(); } public <T> T[] toArray(T[] a) { return deepCopy().toArray(a); } public Spliterator<Map.Entry<K, V>> spliterator() { return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); } } @SuppressWarnings("unchecked") @Override public void forEach(BiConsumer<? super K, ? super V> action) { Objects.requireNonNull(action); int expectedModCount = modCount; Entry<K, V>[] tab = getTable(); for (Entry<K, V> entry : tab) { while (entry != null) { Object key = entry.get(); if (key != null) { action.accept((K) WeakHashMap.unmaskNull(key), entry.value); } entry = entry.next; if (expectedModCount != modCount) { throw new ConcurrentModificationException(); } } } } @SuppressWarnings("unchecked") @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { Objects.requireNonNull(function); int expectedModCount = modCount; Entry<K, V>[] tab = getTable(); ; for (Entry<K, V> entry : tab) { while (entry != null) { Object key = entry.get(); if (key != null) { entry.value = function.apply((K) WeakHashMap.unmaskNull(key), entry.value); } entry = entry.next; if (expectedModCount != modCount) { throw new ConcurrentModificationException(); } } } } /** * Similar form as other hash Spliterators, but skips dead * elements. */ static class WeakHashMapSpliterator<K, V> { final WeakHashMap<K, V> map; WeakHashMap.Entry<K, V> current; // current node int index; // current index, modified on advance/split int fence; // -1 until first use; then one past last index int est; // size estimate int expectedModCount; // for comodification checks WeakHashMapSpliterator(WeakHashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { this.map = m; this.index = origin; this.fence = fence; this.est = est; this.expectedModCount = expectedModCount; } final int getFence() { // initialize fence and size on first use int hi; if ((hi = fence) < 0) { WeakHashMap<K, V> m = map; est = m.size(); expectedModCount = m.modCount; hi = fence = m.table.length; } return hi; } public final long estimateSize() { getFence(); // force init return (long) est; } } static final class KeySpliterator<K, V> extends WeakHashMapSpliterator<K, V> implements Spliterator<K> { KeySpliterator(WeakHashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { super(m, origin, fence, est, expectedModCount); } public KeySpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : new KeySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } public void forEachRemaining(Consumer<? super K> action) { int i, hi, mc; if (action == null) throw new NullPointerException(); WeakHashMap<K, V> m = map; WeakHashMap.Entry<K, V>[] tab = m.table; if ((hi = fence) < 0) { mc = expectedModCount = m.modCount; hi = fence = tab.length; } else mc = expectedModCount; if (tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null)) { WeakHashMap.Entry<K, V> p = current; current = null; // exhaust do { if (p == null) p = tab[i++]; else { Object x = p.get(); p = p.next; if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x); action.accept(k); } } } while (p != null || i < hi); } if (m.modCount != mc) throw new ConcurrentModificationException(); } public boolean tryAdvance(Consumer<? super K> action) { int hi; if (action == null) throw new NullPointerException(); WeakHashMap.Entry<K, V>[] tab = map.table; if (tab.length >= (hi = getFence()) && index >= 0) { while (current != null || index < hi) { if (current == null) current = tab[index++]; else { Object x = current.get(); current = current.next; if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x); action.accept(k); if (map.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } } } } return false; } public int characteristics() { return Spliterator.DISTINCT; } } static final class ValueSpliterator<K, V> extends WeakHashMapSpliterator<K, V> implements Spliterator<V> { ValueSpliterator(WeakHashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { super(m, origin, fence, est, expectedModCount); } public ValueSpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : new ValueSpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } public void forEachRemaining(Consumer<? super V> action) { int i, hi, mc; if (action == null) throw new NullPointerException(); WeakHashMap<K, V> m = map; WeakHashMap.Entry<K, V>[] tab = m.table; if ((hi = fence) < 0) { mc = expectedModCount = m.modCount; hi = fence = tab.length; } else mc = expectedModCount; if (tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null)) { WeakHashMap.Entry<K, V> p = current; current = null; // exhaust do { if (p == null) p = tab[i++]; else { Object x = p.get(); V v = p.value; p = p.next; if (x != null) action.accept(v); } } while (p != null || i < hi); } if (m.modCount != mc) throw new ConcurrentModificationException(); } public boolean tryAdvance(Consumer<? super V> action) { int hi; if (action == null) throw new NullPointerException(); WeakHashMap.Entry<K, V>[] tab = map.table; if (tab.length >= (hi = getFence()) && index >= 0) { while (current != null || index < hi) { if (current == null) current = tab[index++]; else { Object x = current.get(); V v = current.value; current = current.next; if (x != null) { action.accept(v); if (map.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } } } } return false; } public int characteristics() { return 0; } } static final class EntrySpliterator<K, V> extends WeakHashMapSpliterator<K, V> implements Spliterator<Map.Entry<K, V>> { EntrySpliterator(WeakHashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { super(m, origin, fence, est, expectedModCount); } public EntrySpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : new EntrySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { int i, hi, mc; if (action == null) throw new NullPointerException(); WeakHashMap<K, V> m = map; WeakHashMap.Entry<K, V>[] tab = m.table; if ((hi = fence) < 0) { mc = expectedModCount = m.modCount; hi = fence = tab.length; } else mc = expectedModCount; if (tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null)) { WeakHashMap.Entry<K, V> p = current; current = null; // exhaust do { if (p == null) p = tab[i++]; else { Object x = p.get(); V v = p.value; p = p.next; if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x); action.accept(new AbstractMap.SimpleImmutableEntry<>(k, v)); } } } while (p != null || i < hi); } if (m.modCount != mc) throw new ConcurrentModificationException(); } public boolean tryAdvance(Consumer<? super Map.Entry<K, V>> action) { int hi; if (action == null) throw new NullPointerException(); WeakHashMap.Entry<K, V>[] tab = map.table; if (tab.length >= (hi = getFence()) && index >= 0) { while (current != null || index < hi) { if (current == null) current = tab[index++]; else { Object x = current.get(); V v = current.value; current = current.next; if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x); action.accept(new AbstractMap.SimpleImmutableEntry<>(k, v)); if (map.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } } } } return false; } public int characteristics() { return Spliterator.DISTINCT; } } }