Java tutorial
/* * Copyright (c) 2000, 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.reflect.Array; import java.util.function.BiConsumer; import java.util.function.BiFunction; import java.util.function.Consumer; import jdk.internal.access.SharedSecrets; /** * This class implements the {@code Map} interface with a hash table, using * reference-equality in place of object-equality when comparing keys (and * values). In other words, in an {@code IdentityHashMap}, two keys * {@code k1} and {@code k2} are considered equal if and only if * {@code (k1==k2)}. (In normal {@code Map} implementations (like * {@code HashMap}) two keys {@code k1} and {@code k2} are considered equal * if and only if {@code (k1==null ? k2==null : k1.equals(k2))}.) * * <p><b>This class is <i>not</i> a general-purpose {@code Map} * implementation! While this class implements the {@code Map} interface, it * intentionally violates {@code Map's} general contract, which mandates the * use of the {@code equals} method when comparing objects. This class is * designed for use only in the rare cases wherein reference-equality * semantics are required.</b> * * <p>A typical use of this class is <i>topology-preserving object graph * transformations</i>, such as serialization or deep-copying. To perform such * a transformation, a program must maintain a "node table" that keeps track * of all the object references that have already been processed. The node * table must not equate distinct objects even if they happen to be equal. * Another typical use of this class is to maintain <i>proxy objects</i>. For * example, a debugging facility might wish to maintain a proxy object for * each object in the program being debugged. * * <p>This class provides all of the optional map operations, and permits * {@code null} values and the {@code null} key. This class makes no * guarantees as to the order of the map; in particular, it does not guarantee * that the order will remain constant over time. * * <p>This class provides constant-time performance for the basic * operations ({@code get} and {@code put}), assuming the system * identity hash function ({@link System#identityHashCode(Object)}) * disperses elements properly among the buckets. * * <p>This class has one tuning parameter (which affects performance but not * semantics): <i>expected maximum size</i>. This parameter is the maximum * number of key-value mappings that the map is expected to hold. Internally, * this parameter is used to determine the number of buckets initially * comprising the hash table. The precise relationship between the expected * maximum size and the number of buckets is unspecified. * * <p>If the size of the map (the number of key-value mappings) sufficiently * exceeds the expected maximum size, the number of buckets is increased. * Increasing the number of buckets ("rehashing") may be fairly expensive, so * it pays to create identity hash maps with a sufficiently large expected * maximum size. On the other hand, iteration over collection views requires * time proportional to the number of buckets in the hash table, so it * pays not to set the expected maximum size too high if you are especially * concerned with iteration performance or memory usage. * * <p><strong>Note that this implementation is not synchronized.</strong> * If multiple threads access an identity hash map concurrently, and at * least one of the threads modifies the map structurally, it <i>must</i> * be synchronized externally. (A structural modification is any operation * that adds or deletes one or more mappings; merely changing the value * associated with a key that an instance already contains is not a * structural modification.) 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 IdentityHashMap(...));</pre> * * <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>fail-fast iterators should be used only * to detect bugs.</i> * * <p>Implementation note: This is a simple <i>linear-probe</i> hash table, * as described for example in texts by Sedgewick and Knuth. The array * alternates holding keys and values. (This has better locality for large * tables than does using separate arrays.) For many JRE implementations * and operation mixes, this class will yield better performance than * {@link HashMap} (which uses <i>chaining</i> rather than linear-probing). * * <p>This class is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @see System#identityHashCode(Object) * @see Object#hashCode() * @see Collection * @see Map * @see HashMap * @see TreeMap * @author Doug Lea and Josh Bloch * @since 1.4 */ public class IdentityHashMap<K, V> extends AbstractMap<K, V> implements Map<K, V>, java.io.Serializable, Cloneable { /** * The initial capacity used by the no-args constructor. * MUST be a power of two. The value 32 corresponds to the * (specified) expected maximum size of 21, given a load factor * of 2/3. */ private static final int DEFAULT_CAPACITY = 32; /** * The minimum capacity, used if a lower value is implicitly specified * by either of the constructors with arguments. The value 4 corresponds * to an expected maximum size of 2, given a load factor of 2/3. * MUST be a power of two. */ private static final int MINIMUM_CAPACITY = 4; /** * 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<<29. * * In fact, the map can hold no more than MAXIMUM_CAPACITY-1 items * because it has to have at least one slot with the key == null * in order to avoid infinite loops in get(), put(), remove() */ private static final int MAXIMUM_CAPACITY = 1 << 29; /** * The table, resized as necessary. Length MUST always be a power of two. */ transient Object[] table; // non-private to simplify nested class access /** * The number of key-value mappings contained in this identity hash map. * * @serial */ int size; /** * The number of modifications, to support fast-fail iterators */ transient int modCount; /** * Value representing null keys inside tables. */ 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 final Object unmaskNull(Object key) { return (key == NULL_KEY ? null : key); } /** * Constructs a new, empty identity hash map with a default expected * maximum size (21). */ public IdentityHashMap() { init(DEFAULT_CAPACITY); } /** * Constructs a new, empty map with the specified expected maximum size. * Putting more than the expected number of key-value mappings into * the map may cause the internal data structure to grow, which may be * somewhat time-consuming. * * @param expectedMaxSize the expected maximum size of the map * @throws IllegalArgumentException if {@code expectedMaxSize} is negative */ public IdentityHashMap(int expectedMaxSize) { if (expectedMaxSize < 0) throw new IllegalArgumentException("expectedMaxSize is negative: " + expectedMaxSize); init(capacity(expectedMaxSize)); } /** * Returns the appropriate capacity for the given expected maximum size. * Returns the smallest power of two between MINIMUM_CAPACITY and * MAXIMUM_CAPACITY, inclusive, that is greater than (3 * * expectedMaxSize)/2, if such a number exists. Otherwise returns * MAXIMUM_CAPACITY. */ private static int capacity(int expectedMaxSize) { // assert expectedMaxSize >= 0; return (expectedMaxSize > MAXIMUM_CAPACITY / 3) ? MAXIMUM_CAPACITY : (expectedMaxSize <= 2 * MINIMUM_CAPACITY / 3) ? MINIMUM_CAPACITY : Integer.highestOneBit(expectedMaxSize + (expectedMaxSize << 1)); } /** * Initializes object to be an empty map with the specified initial * capacity, which is assumed to be a power of two between * MINIMUM_CAPACITY and MAXIMUM_CAPACITY inclusive. */ private void init(int initCapacity) { // assert (initCapacity & -initCapacity) == initCapacity; // power of 2 // assert initCapacity >= MINIMUM_CAPACITY; // assert initCapacity <= MAXIMUM_CAPACITY; table = new Object[2 * initCapacity]; } /** * Constructs a new identity hash map containing the keys-value mappings * in the specified map. * * @param m the map whose mappings are to be placed into this map * @throws NullPointerException if the specified map is null */ public IdentityHashMap(Map<? extends K, ? extends V> m) { // Allow for a bit of growth this((int) ((1 + m.size()) * 1.1)); putAll(m); } /** * Returns the number of key-value mappings in this identity hash map. * * @return the number of key-value mappings in this map */ public int size() { return size; } /** * Returns {@code true} if this identity hash map contains no key-value * mappings. * * @return {@code true} if this identity hash map contains no key-value * mappings */ public boolean isEmpty() { return size == 0; } /** * Returns index for Object x. */ private static int hash(Object x, int length) { int h = System.identityHashCode(x); // Multiply by -127, and left-shift to use least bit as part of hash return ((h << 1) - (h << 8)) & (length - 1); } /** * Circularly traverses table of size len. */ private static int nextKeyIndex(int i, int len) { return (i + 2 < len ? i + 2 : 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 (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) */ @SuppressWarnings("unchecked") public V get(Object key) { Object k = maskNull(key); Object[] tab = table; int len = tab.length; int i = hash(k, len); while (true) { Object item = tab[i]; if (item == k) return (V) tab[i + 1]; if (item == null) return null; i = nextKeyIndex(i, len); } } /** * Tests whether the specified object reference is a key in this identity * hash map. * * @param key possible key * @return {@code true} if the specified object reference is a key * in this map * @see #containsValue(Object) */ public boolean containsKey(Object key) { Object k = maskNull(key); Object[] tab = table; int len = tab.length; int i = hash(k, len); while (true) { Object item = tab[i]; if (item == k) return true; if (item == null) return false; i = nextKeyIndex(i, len); } } /** * Tests whether the specified object reference is a value in this identity * hash map. * * @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 object reference * @see #containsKey(Object) */ public boolean containsValue(Object value) { Object[] tab = table; for (int i = 1; i < tab.length; i += 2) if (tab[i] == value && tab[i - 1] != null) return true; return false; } /** * Tests if the specified key-value mapping is in the map. * * @param key possible key * @param value possible value * @return {@code true} if and only if the specified key-value * mapping is in the map */ private boolean containsMapping(Object key, Object value) { Object k = maskNull(key); Object[] tab = table; int len = tab.length; int i = hash(k, len); while (true) { Object item = tab[i]; if (item == k) return tab[i + 1] == value; if (item == null) return false; i = nextKeyIndex(i, len); } } /** * Associates the specified value with the specified key in this identity * hash map. If the map previously contained a mapping for the key, the * old value is replaced. * * @param key the key with which the specified value is to be associated * @param value the 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}.) * @see Object#equals(Object) * @see #get(Object) * @see #containsKey(Object) */ public V put(K key, V value) { final Object k = maskNull(key); retryAfterResize: for (;;) { final Object[] tab = table; final int len = tab.length; int i = hash(k, len); for (Object item; (item = tab[i]) != null; i = nextKeyIndex(i, len)) { if (item == k) { @SuppressWarnings("unchecked") V oldValue = (V) tab[i + 1]; tab[i + 1] = value; return oldValue; } } final int s = size + 1; // Use optimized form of 3 * s. // Next capacity is len, 2 * current capacity. if (s + (s << 1) > len && resize(len)) continue retryAfterResize; modCount++; tab[i] = k; tab[i + 1] = value; size = s; return null; } } /** * Resizes the table if necessary to hold given capacity. * * @param newCapacity the new capacity, must be a power of two. * @return whether a resize did in fact take place */ private boolean resize(int newCapacity) { // assert (newCapacity & -newCapacity) == newCapacity; // power of 2 int newLength = newCapacity * 2; Object[] oldTable = table; int oldLength = oldTable.length; if (oldLength == 2 * MAXIMUM_CAPACITY) { // can't expand any further if (size == MAXIMUM_CAPACITY - 1) throw new IllegalStateException("Capacity exhausted."); return false; } if (oldLength >= newLength) return false; Object[] newTable = new Object[newLength]; for (int j = 0; j < oldLength; j += 2) { Object key = oldTable[j]; if (key != null) { Object value = oldTable[j + 1]; oldTable[j] = null; oldTable[j + 1] = null; int i = hash(key, newLength); while (newTable[i] != null) i = nextKeyIndex(i, newLength); newTable[i] = key; newTable[i + 1] = value; } } table = newTable; return true; } /** * 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 n = m.size(); if (n == 0) return; if (n > size) resize(capacity(n)); // conservatively pre-expand for (Entry<? extends K, ? extends V> e : m.entrySet()) put(e.getKey(), e.getValue()); } /** * Removes the mapping for this key from this map if present. * * @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}. * (A {@code null} return can also indicate that the map * previously associated {@code null} with {@code key}.) */ public V remove(Object key) { Object k = maskNull(key); Object[] tab = table; int len = tab.length; int i = hash(k, len); while (true) { Object item = tab[i]; if (item == k) { modCount++; size--; @SuppressWarnings("unchecked") V oldValue = (V) tab[i + 1]; tab[i + 1] = null; tab[i] = null; closeDeletion(i); return oldValue; } if (item == null) return null; i = nextKeyIndex(i, len); } } /** * Removes the specified key-value mapping from the map if it is present. * * @param key possible key * @param value possible value * @return {@code true} if and only if the specified key-value * mapping was in the map */ private boolean removeMapping(Object key, Object value) { Object k = maskNull(key); Object[] tab = table; int len = tab.length; int i = hash(k, len); while (true) { Object item = tab[i]; if (item == k) { if (tab[i + 1] != value) return false; modCount++; size--; tab[i] = null; tab[i + 1] = null; closeDeletion(i); return true; } if (item == null) return false; i = nextKeyIndex(i, len); } } /** * Rehash all possibly-colliding entries following a * deletion. This preserves the linear-probe * collision properties required by get, put, etc. * * @param d the index of a newly empty deleted slot */ private void closeDeletion(int d) { // Adapted from Knuth Section 6.4 Algorithm R Object[] tab = table; int len = tab.length; // Look for items to swap into newly vacated slot // starting at index immediately following deletion, // and continuing until a null slot is seen, indicating // the end of a run of possibly-colliding keys. Object item; for (int i = nextKeyIndex(d, len); (item = tab[i]) != null; i = nextKeyIndex(i, len)) { // The following test triggers if the item at slot i (which // hashes to be at slot r) should take the spot vacated by d. // If so, we swap it in, and then continue with d now at the // newly vacated i. This process will terminate when we hit // the null slot at the end of this run. // The test is messy because we are using a circular table. int r = hash(item, len); if ((i < r && (r <= d || d <= i)) || (r <= d && d <= i)) { tab[d] = item; tab[d + 1] = tab[i + 1]; tab[i] = null; tab[i + 1] = null; d = i; } } } /** * Removes all of the mappings from this map. * The map will be empty after this call returns. */ public void clear() { modCount++; Object[] tab = table; for (int i = 0; i < tab.length; i++) tab[i] = null; size = 0; } /** * Compares the specified object with this map for equality. Returns * {@code true} if the given object is also a map and the two maps * represent identical object-reference mappings. More formally, this * map is equal to another map {@code m} if and only if * {@code this.entrySet().equals(m.entrySet())}. * * <p><b>Owing to the reference-equality-based semantics of this map it is * possible that the symmetry and transitivity requirements of the * {@code Object.equals} contract may be violated if this map is compared * to a normal map. However, the {@code Object.equals} contract is * guaranteed to hold among {@code IdentityHashMap} instances.</b> * * @param o object to be compared for equality with this map * @return {@code true} if the specified object is equal to this map * @see Object#equals(Object) */ public boolean equals(Object o) { if (o == this) { return true; } else if (o instanceof IdentityHashMap) { IdentityHashMap<?, ?> m = (IdentityHashMap<?, ?>) o; if (m.size() != size) return false; Object[] tab = m.table; for (int i = 0; i < tab.length; i += 2) { Object k = tab[i]; if (k != null && !containsMapping(k, tab[i + 1])) return false; } return true; } else if (o instanceof Map) { Map<?, ?> m = (Map<?, ?>) o; return entrySet().equals(m.entrySet()); } else { return false; // o is not a Map } } /** * Returns the hash code value for this map. The hash code of a map is * defined to be the sum of the hash codes of each entry in the map's * {@code entrySet()} view. This ensures that {@code m1.equals(m2)} * implies that {@code m1.hashCode()==m2.hashCode()} for any two * {@code IdentityHashMap} instances {@code m1} and {@code m2}, as * required by the general contract of {@link Object#hashCode}. * * <p><b>Owing to the reference-equality-based semantics of the * {@code Map.Entry} instances in the set returned by this map's * {@code entrySet} method, it is possible that the contractual * requirement of {@code Object.hashCode} mentioned in the previous * paragraph will be violated if one of the two objects being compared is * an {@code IdentityHashMap} instance and the other is a normal map.</b> * * @return the hash code value for this map * @see Object#equals(Object) * @see #equals(Object) */ public int hashCode() { int result = 0; Object[] tab = table; for (int i = 0; i < tab.length; i += 2) { Object key = tab[i]; if (key != null) { Object k = unmaskNull(key); result += System.identityHashCode(k) ^ System.identityHashCode(tab[i + 1]); } } return result; } /** * Returns a shallow copy of this identity hash map: the keys and values * themselves are not cloned. * * @return a shallow copy of this map */ public Object clone() { try { IdentityHashMap<?, ?> m = (IdentityHashMap<?, ?>) super.clone(); m.entrySet = null; m.table = table.clone(); return m; } catch (CloneNotSupportedException e) { throw new InternalError(e); } } private abstract class IdentityHashMapIterator<T> implements Iterator<T> { int index = (size != 0 ? 0 : table.length); // current slot. int expectedModCount = modCount; // to support fast-fail int lastReturnedIndex = -1; // to allow remove() boolean indexValid; // To avoid unnecessary next computation Object[] traversalTable = table; // reference to main table or copy public boolean hasNext() { Object[] tab = traversalTable; for (int i = index; i < tab.length; i += 2) { Object key = tab[i]; if (key != null) { index = i; return indexValid = true; } } index = tab.length; return false; } protected int nextIndex() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); if (!indexValid && !hasNext()) throw new NoSuchElementException(); indexValid = false; lastReturnedIndex = index; index += 2; return lastReturnedIndex; } public void remove() { if (lastReturnedIndex == -1) throw new IllegalStateException(); if (modCount != expectedModCount) throw new ConcurrentModificationException(); expectedModCount = ++modCount; int deletedSlot = lastReturnedIndex; lastReturnedIndex = -1; // back up index to revisit new contents after deletion index = deletedSlot; indexValid = false; // Removal code proceeds as in closeDeletion except that // it must catch the rare case where an element already // seen is swapped into a vacant slot that will be later // traversed by this iterator. We cannot allow future // next() calls to return it again. The likelihood of // this occurring under 2/3 load factor is very slim, but // when it does happen, we must make a copy of the rest of // the table to use for the rest of the traversal. Since // this can only happen when we are near the end of the table, // even in these rare cases, this is not very expensive in // time or space. Object[] tab = traversalTable; int len = tab.length; int d = deletedSlot; Object key = tab[d]; tab[d] = null; // vacate the slot tab[d + 1] = null; // If traversing a copy, remove in real table. // We can skip gap-closure on copy. if (tab != IdentityHashMap.this.table) { IdentityHashMap.this.remove(key); expectedModCount = modCount; return; } size--; Object item; for (int i = nextKeyIndex(d, len); (item = tab[i]) != null; i = nextKeyIndex(i, len)) { int r = hash(item, len); // See closeDeletion for explanation of this conditional if ((i < r && (r <= d || d <= i)) || (r <= d && d <= i)) { // If we are about to swap an already-seen element // into a slot that may later be returned by next(), // then clone the rest of table for use in future // next() calls. It is OK that our copy will have // a gap in the "wrong" place, since it will never // be used for searching anyway. if (i < deletedSlot && d >= deletedSlot && traversalTable == IdentityHashMap.this.table) { int remaining = len - deletedSlot; Object[] newTable = new Object[remaining]; System.arraycopy(tab, deletedSlot, newTable, 0, remaining); traversalTable = newTable; index = 0; } tab[d] = item; tab[d + 1] = tab[i + 1]; tab[i] = null; tab[i + 1] = null; d = i; } } } } private class KeyIterator extends IdentityHashMapIterator<K> { @SuppressWarnings("unchecked") public K next() { return (K) unmaskNull(traversalTable[nextIndex()]); } } private class ValueIterator extends IdentityHashMapIterator<V> { @SuppressWarnings("unchecked") public V next() { return (V) traversalTable[nextIndex() + 1]; } } private class EntryIterator extends IdentityHashMapIterator<Map.Entry<K, V>> { private Entry lastReturnedEntry; public Map.Entry<K, V> next() { lastReturnedEntry = new Entry(nextIndex()); return lastReturnedEntry; } public void remove() { lastReturnedIndex = ((null == lastReturnedEntry) ? -1 : lastReturnedEntry.index); super.remove(); lastReturnedEntry.index = lastReturnedIndex; lastReturnedEntry = null; } private class Entry implements Map.Entry<K, V> { private int index; private Entry(int index) { this.index = index; } @SuppressWarnings("unchecked") public K getKey() { checkIndexForEntryUse(); return (K) unmaskNull(traversalTable[index]); } @SuppressWarnings("unchecked") public V getValue() { checkIndexForEntryUse(); return (V) traversalTable[index + 1]; } @SuppressWarnings("unchecked") public V setValue(V value) { checkIndexForEntryUse(); V oldValue = (V) traversalTable[index + 1]; traversalTable[index + 1] = value; // if shadowing, force into main table if (traversalTable != IdentityHashMap.this.table) put((K) traversalTable[index], value); return oldValue; } public boolean equals(Object o) { if (index < 0) return super.equals(o); if (!(o instanceof Map.Entry)) return false; Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; return (e.getKey() == unmaskNull(traversalTable[index]) && e.getValue() == traversalTable[index + 1]); } public int hashCode() { if (lastReturnedIndex < 0) return super.hashCode(); return (System.identityHashCode(unmaskNull(traversalTable[index])) ^ System.identityHashCode(traversalTable[index + 1])); } public String toString() { if (index < 0) return super.toString(); return (unmaskNull(traversalTable[index]) + "=" + traversalTable[index + 1]); } private void checkIndexForEntryUse() { if (index < 0) throw new IllegalStateException("Entry was removed"); } } } // Views /** * This field is initialized to contain an instance of the entry set * view the first time this view is requested. The view is stateless, * so there's no reason to create more than one. */ private transient Set<Map.Entry<K, V>> entrySet; /** * Returns an identity-based 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, 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} methods. It does not support the {@code add} or * {@code addAll} methods. * * <p><b>While the object returned by this method implements the * {@code Set} interface, it does <i>not</i> obey {@code Set's} general * contract. Like its backing map, the set returned by this method * defines element equality as reference-equality rather than * object-equality. This affects the behavior of its {@code contains}, * {@code remove}, {@code containsAll}, {@code equals}, and * {@code hashCode} methods.</b> * * <p><b>The {@code equals} method of the returned set returns {@code true} * only if the specified object is a set containing exactly the same * object references as the returned set. The symmetry and transitivity * requirements of the {@code Object.equals} contract may be violated if * the set returned by this method is compared to a normal set. However, * the {@code Object.equals} contract is guaranteed to hold among sets * returned by this method.</b> * * <p>The {@code hashCode} method of the returned set returns the sum of * the <i>identity hashcodes</i> of the elements in the set, rather than * the sum of their hashcodes. This is mandated by the change in the * semantics of the {@code equals} method, in order to enforce the * general contract of the {@code Object.hashCode} method among sets * returned by this method. * * @return an identity-based set view of the keys contained in this map * @see Object#equals(Object) * @see System#identityHashCode(Object) */ 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 size; } public boolean contains(Object o) { return containsKey(o); } public boolean remove(Object o) { int oldSize = size; IdentityHashMap.this.remove(o); return size != oldSize; } /* * Must revert from AbstractSet's impl to AbstractCollection's, as * the former contains an optimization that results in incorrect * behavior when c is a smaller "normal" (non-identity-based) Set. */ public boolean removeAll(Collection<?> c) { Objects.requireNonNull(c); boolean modified = false; for (Iterator<K> i = iterator(); i.hasNext();) { if (c.contains(i.next())) { i.remove(); modified = true; } } return modified; } public void clear() { IdentityHashMap.this.clear(); } public int hashCode() { int result = 0; for (K key : this) result += System.identityHashCode(key); return result; } public Object[] toArray() { return toArray(new Object[0]); } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { int expectedModCount = modCount; int size = size(); if (a.length < size) a = (T[]) Array.newInstance(a.getClass().getComponentType(), size); Object[] tab = table; int ti = 0; for (int si = 0; si < tab.length; si += 2) { Object key; if ((key = tab[si]) != null) { // key present ? // more elements than expected -> concurrent modification from other thread if (ti >= size) { throw new ConcurrentModificationException(); } a[ti++] = (T) unmaskNull(key); // unmask key } } // fewer elements than expected or concurrent modification from other thread detected if (ti < size || expectedModCount != modCount) { throw new ConcurrentModificationException(); } // final null marker as per spec if (ti < a.length) { a[ti] = null; } return a; } public Spliterator<K> spliterator() { return new KeySpliterator<>(IdentityHashMap.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, * 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} methods. It does not * support the {@code add} or {@code addAll} methods. * * <p><b>While the object returned by this method implements the * {@code Collection} interface, it does <i>not</i> obey * {@code Collection's} general contract. Like its backing map, * the collection returned by this method defines element equality as * reference-equality rather than object-equality. This affects the * behavior of its {@code contains}, {@code remove} and * {@code containsAll} methods.</b> */ 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 size; } public boolean contains(Object o) { return containsValue(o); } public boolean remove(Object o) { for (Iterator<V> i = iterator(); i.hasNext();) { if (i.next() == o) { i.remove(); return true; } } return false; } public void clear() { IdentityHashMap.this.clear(); } public Object[] toArray() { return toArray(new Object[0]); } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { int expectedModCount = modCount; int size = size(); if (a.length < size) a = (T[]) Array.newInstance(a.getClass().getComponentType(), size); Object[] tab = table; int ti = 0; for (int si = 0; si < tab.length; si += 2) { if (tab[si] != null) { // key present ? // more elements than expected -> concurrent modification from other thread if (ti >= size) { throw new ConcurrentModificationException(); } a[ti++] = (T) tab[si + 1]; // copy value } } // fewer elements than expected or concurrent modification from other thread detected if (ti < size || expectedModCount != modCount) { throw new ConcurrentModificationException(); } // final null marker as per spec if (ti < a.length) { a[ti] = null; } return a; } public Spliterator<V> spliterator() { return new ValueSpliterator<>(IdentityHashMap.this, 0, -1, 0, 0); } } /** * Returns a {@link Set} view of the mappings contained in this map. * Each element in the returned set is a reference-equality-based * {@code Map.Entry}. 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, * 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} * methods. It does not support the {@code add} or * {@code addAll} methods. * * <p>Like the backing map, the {@code Map.Entry} objects in the set * returned by this method define key and value equality as * reference-equality rather than object-equality. This affects the * behavior of the {@code equals} and {@code hashCode} methods of these * {@code Map.Entry} objects. A reference-equality based {@code Map.Entry * e} is equal to an object {@code o} if and only if {@code o} is a * {@code Map.Entry} and {@code e.getKey()==o.getKey() && * e.getValue()==o.getValue()}. To accommodate these equals * semantics, the {@code hashCode} method returns * {@code System.identityHashCode(e.getKey()) ^ * System.identityHashCode(e.getValue())}. * * <p><b>Owing to the reference-equality-based semantics of the * {@code Map.Entry} instances in the set returned by this method, * it is possible that the symmetry and transitivity requirements of * the {@link Object#equals(Object)} contract may be violated if any of * the entries in the set is compared to a normal map entry, or if * the set returned by this method is compared to a set of normal map * entries (such as would be returned by a call to this method on a normal * map). However, the {@code Object.equals} contract is guaranteed to * hold among identity-based map entries, and among sets of such entries. * </b> * * @return a set view of the identity-mappings contained in this map */ public Set<Map.Entry<K, V>> entrySet() { Set<Map.Entry<K, V>> es = entrySet; if (es != null) return es; else return 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<?, ?> entry = (Map.Entry<?, ?>) o; return containsMapping(entry.getKey(), entry.getValue()); } public boolean remove(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o; return removeMapping(entry.getKey(), entry.getValue()); } public int size() { return size; } public void clear() { IdentityHashMap.this.clear(); } /* * Must revert from AbstractSet's impl to AbstractCollection's, as * the former contains an optimization that results in incorrect * behavior when c is a smaller "normal" (non-identity-based) Set. */ public boolean removeAll(Collection<?> c) { Objects.requireNonNull(c); boolean modified = false; for (Iterator<Map.Entry<K, V>> i = iterator(); i.hasNext();) { if (c.contains(i.next())) { i.remove(); modified = true; } } return modified; } public Object[] toArray() { return toArray(new Object[0]); } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { int expectedModCount = modCount; int size = size(); if (a.length < size) a = (T[]) Array.newInstance(a.getClass().getComponentType(), size); Object[] tab = table; int ti = 0; for (int si = 0; si < tab.length; si += 2) { Object key; if ((key = tab[si]) != null) { // key present ? // more elements than expected -> concurrent modification from other thread if (ti >= size) { throw new ConcurrentModificationException(); } a[ti++] = (T) new AbstractMap.SimpleEntry<>(unmaskNull(key), tab[si + 1]); } } // fewer elements than expected or concurrent modification from other thread detected if (ti < size || expectedModCount != modCount) { throw new ConcurrentModificationException(); } // final null marker as per spec if (ti < a.length) { a[ti] = null; } return a; } public Spliterator<Map.Entry<K, V>> spliterator() { return new EntrySpliterator<>(IdentityHashMap.this, 0, -1, 0, 0); } } private static final long serialVersionUID = 8188218128353913216L; /** * Saves the state of the {@code IdentityHashMap} instance to a stream * (i.e., serializes it). * * @serialData The <i>size</i> of the HashMap (the number of key-value * mappings) ({@code int}), followed by the key (Object) and * value (Object) for each key-value mapping represented by the * IdentityHashMap. The key-value mappings are emitted in no * particular order. */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { // Write out and any hidden stuff s.defaultWriteObject(); // Write out size (number of Mappings) s.writeInt(size); // Write out keys and values (alternating) Object[] tab = table; for (int i = 0; i < tab.length; i += 2) { Object key = tab[i]; if (key != null) { s.writeObject(unmaskNull(key)); s.writeObject(tab[i + 1]); } } } /** * Reconstitutes the {@code IdentityHashMap} instance from a stream (i.e., * deserializes it). */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in any hidden stuff s.defaultReadObject(); // Read in size (number of Mappings) int size = s.readInt(); if (size < 0) throw new java.io.StreamCorruptedException("Illegal mappings count: " + size); int cap = capacity(size); SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, cap); init(cap); // Read the keys and values, and put the mappings in the table for (int i = 0; i < size; i++) { @SuppressWarnings("unchecked") K key = (K) s.readObject(); @SuppressWarnings("unchecked") V value = (V) s.readObject(); putForCreate(key, value); } } /** * The put method for readObject. It does not resize the table, * update modCount, etc. */ private void putForCreate(K key, V value) throws java.io.StreamCorruptedException { Object k = maskNull(key); Object[] tab = table; int len = tab.length; int i = hash(k, len); Object item; while ((item = tab[i]) != null) { if (item == k) throw new java.io.StreamCorruptedException(); i = nextKeyIndex(i, len); } tab[i] = k; tab[i + 1] = value; } @SuppressWarnings("unchecked") @Override public void forEach(BiConsumer<? super K, ? super V> action) { Objects.requireNonNull(action); int expectedModCount = modCount; Object[] t = table; for (int index = 0; index < t.length; index += 2) { Object k = t[index]; if (k != null) { action.accept((K) unmaskNull(k), (V) t[index + 1]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } } } @SuppressWarnings("unchecked") @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { Objects.requireNonNull(function); int expectedModCount = modCount; Object[] t = table; for (int index = 0; index < t.length; index += 2) { Object k = t[index]; if (k != null) { t[index + 1] = function.apply((K) unmaskNull(k), (V) t[index + 1]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } } } /** * Similar form as array-based Spliterators, but skips blank elements, * and guestimates size as decreasing by half per split. */ static class IdentityHashMapSpliterator<K, V> { final IdentityHashMap<K, V> map; 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; // initialized when fence set IdentityHashMapSpliterator(IdentityHashMap<K, V> map, int origin, int fence, int est, int expectedModCount) { this.map = map; 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) { est = map.size; expectedModCount = map.modCount; hi = fence = map.table.length; } return hi; } public final long estimateSize() { getFence(); // force init return (long) est; } } static final class KeySpliterator<K, V> extends IdentityHashMapSpliterator<K, V> implements Spliterator<K> { KeySpliterator(IdentityHashMap<K, V> map, int origin, int fence, int est, int expectedModCount) { super(map, origin, fence, est, expectedModCount); } public KeySpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = ((lo + hi) >>> 1) & ~1; return (lo >= mid) ? null : new KeySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } @SuppressWarnings("unchecked") public void forEachRemaining(Consumer<? super K> action) { if (action == null) throw new NullPointerException(); int i, hi, mc; Object key; IdentityHashMap<K, V> m; Object[] a; if ((m = map) != null && (a = m.table) != null && (i = index) >= 0 && (index = hi = getFence()) <= a.length) { for (; i < hi; i += 2) { if ((key = a[i]) != null) action.accept((K) unmaskNull(key)); } if (m.modCount == expectedModCount) return; } throw new ConcurrentModificationException(); } @SuppressWarnings("unchecked") public boolean tryAdvance(Consumer<? super K> action) { if (action == null) throw new NullPointerException(); Object[] a = map.table; int hi = getFence(); while (index < hi) { Object key = a[index]; index += 2; if (key != null) { action.accept((K) unmaskNull(key)); if (map.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } } return false; } public int characteristics() { return (fence < 0 || est == map.size ? SIZED : 0) | Spliterator.DISTINCT; } } static final class ValueSpliterator<K, V> extends IdentityHashMapSpliterator<K, V> implements Spliterator<V> { ValueSpliterator(IdentityHashMap<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) & ~1; return (lo >= mid) ? null : new ValueSpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } public void forEachRemaining(Consumer<? super V> action) { if (action == null) throw new NullPointerException(); int i, hi, mc; IdentityHashMap<K, V> m; Object[] a; if ((m = map) != null && (a = m.table) != null && (i = index) >= 0 && (index = hi = getFence()) <= a.length) { for (; i < hi; i += 2) { if (a[i] != null) { @SuppressWarnings("unchecked") V v = (V) a[i + 1]; action.accept(v); } } if (m.modCount == expectedModCount) return; } throw new ConcurrentModificationException(); } public boolean tryAdvance(Consumer<? super V> action) { if (action == null) throw new NullPointerException(); Object[] a = map.table; int hi = getFence(); while (index < hi) { Object key = a[index]; @SuppressWarnings("unchecked") V v = (V) a[index + 1]; index += 2; if (key != null) { action.accept(v); if (map.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } } return false; } public int characteristics() { return (fence < 0 || est == map.size ? SIZED : 0); } } static final class EntrySpliterator<K, V> extends IdentityHashMapSpliterator<K, V> implements Spliterator<Map.Entry<K, V>> { EntrySpliterator(IdentityHashMap<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) & ~1; return (lo >= mid) ? null : new EntrySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { if (action == null) throw new NullPointerException(); int i, hi, mc; IdentityHashMap<K, V> m; Object[] a; if ((m = map) != null && (a = m.table) != null && (i = index) >= 0 && (index = hi = getFence()) <= a.length) { for (; i < hi; i += 2) { Object key = a[i]; if (key != null) { @SuppressWarnings("unchecked") K k = (K) unmaskNull(key); @SuppressWarnings("unchecked") V v = (V) a[i + 1]; action.accept(new AbstractMap.SimpleImmutableEntry<>(k, v)); } } if (m.modCount == expectedModCount) return; } throw new ConcurrentModificationException(); } public boolean tryAdvance(Consumer<? super Map.Entry<K, V>> action) { if (action == null) throw new NullPointerException(); Object[] a = map.table; int hi = getFence(); while (index < hi) { Object key = a[index]; @SuppressWarnings("unchecked") V v = (V) a[index + 1]; index += 2; if (key != null) { @SuppressWarnings("unchecked") K k = (K) unmaskNull(key); action.accept(new AbstractMap.SimpleImmutableEntry<>(k, v)); if (map.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } } return false; } public int characteristics() { return (fence < 0 || est == map.size ? SIZED : 0) | Spliterator.DISTINCT; } } }