/*
 * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

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) (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.
 */
 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;
 }
 }

}