org.zoodb.jdo.internal.util.WeakIdentityHashMap Maven / Gradle / Ivy
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package org.zoodb.jdo.internal.util;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* This is a remodelled version of the WeakHashMap that uses object identity
* rather than equality.
*
* A hashtable-based Map implementation with weak keys.
* An entry in a WeakHashMap will automatically be removed when
* its key is no longer in ordinary use. More precisely, the presence of a
* mapping for a given key will not prevent the key from being discarded by the
* garbage collector, that is, made finalizable, finalized, and then reclaimed.
* When a key has been discarded its entry is effectively removed from the map,
* so this class behaves somewhat differently than other Map
* implementations.
*
* Both null values and the null key are supported. This class has
* performance characteristics similar to those of the HashMap
* class, and has the same efficiency parameters of initial capacity
* and load factor.
*
*
Like most collection classes, this class is not synchronized. A
* synchronized WeakHashMap may be constructed using the
* Collections.synchronizedMap method.
*
*
This class is intended primarily for use with key objects whose
* equals methods test for object identity using the
* == operator. Once such a key is discarded it can never be
* recreated, so it is impossible to do a lookup of that key in a
* WeakHashMap at some later time and be surprised that its entry
* has been removed. This class will work perfectly well with key objects
* whose equals methods are not based upon object identity, such
* as String instances. With such recreatable key objects,
* however, the automatic removal of WeakHashMap entries whose
* keys have been discarded may prove to be confusing.
*
*
The behavior of the WeakHashMap class depends in part upon
* the actions of the garbage collector, so several familiar (though not
* required) Map invariants do not hold for this class. Because
* the garbage collector may discard keys at any time, a
* WeakHashMap may behave as though an unknown thread is silently
* removing entries. In particular, even if you synchronize on a
* WeakHashMap instance and invoke none of its mutator methods, it
* is possible for the size method to return smaller values over
* time, for the isEmpty method to return false and
* then true, for the containsKey method to return
* true and later false for a given key, for the
* get method to return a value for a given key but later return
* null, for the put method to return
* null and the remove method to return
* false for a key that previously appeared to be in the map, and
* for successive examinations of the key set, the value set, and the entry set
* to yield successively smaller numbers of elements.
*
*
Each key object in a WeakHashMap is stored indirectly as
* the referent of a weak reference. Therefore a key will automatically be
* removed only after the weak references to it, both inside and outside of the
* map, have been cleared by the garbage collector.
*
*
Implementation note: The value objects in a
* WeakHashMap are held by ordinary strong references. Thus care
* should be taken to ensure that value objects do not strongly refer to their
* own keys, either directly or indirectly, since that will prevent the keys
* from being discarded. Note that a value object may refer indirectly to its
* key via the WeakHashMap itself; that is, a value object may
* strongly refer to some other key object whose associated value object, in
* turn, strongly refers to the key of the first value object. One way
* to deal with this is to wrap values themselves within
* WeakReferences before
* inserting, as in: m.put(key, new WeakReference(value)),
* and then unwrapping upon each get.
*
*
The iterators returned by all of this class's "collection view methods"
* are fail-fast: if the map is structurally modified at any time after
* the iterator is created, in any way except through the iterator's own
* remove or add methods, the iterator will throw a
* ConcurrentModificationException. Thus, in the face of concurrent
* modification, the iterator fails quickly and cleanly, rather than risking
* arbitrary, non-deterministic behavior at an undetermined time in the
* future.
*
*
Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw ConcurrentModificationException on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: the fail-fast behavior of iterators
* should be used only to detect bugs.
*
*
This class is a member of the
*
* Java Collections Framework.
* @param
* @param
*
* @version 1.30, 02/19/04
* @author Doug Lea
* @author Josh Bloch
* @author Mark Reinhold
* @since 1.2
* @see java.util.HashMap
* @see java.lang.ref.WeakReference
*/
public class WeakIdentityHashMap //extends AbstractMap
implements Map {
/**
* The default initial capacity -- MUST be a power of two.
*/
private static final int DEFAULT_INITIAL_CAPACITY = 16;
/**
* The maximum capacity, used if a higher value is implicitly specified
* by either of the constructors with arguments.
* MUST be a power of two <= 1<<30.
*/
private static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The load fast 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.
*/
private Entry[] table;
/**
* The number of key-value mappings contained in this weak hash map.
*/
private int size;
/**
* The next size value at which to resize (capacity * load factor).
*/
private int threshold;
/**
* The load factor for the hash table.
*/
private final float loadFactor;
/**
* Reference queue for cleared WeakEntries
*/
private final ReferenceQueue queue = new ReferenceQueue();
/**
* The number of times this HashMap has been structurally modified
* Structural modifications are those that change the number of mappings in
* the HashMap or otherwise modify its internal structure (e.g.,
* rehash). This field is used to make iterators on Collection-views of
* the HashMap fail-fast. (See ConcurrentModificationException).
*/
private volatile int modCount;
/**
* Constructs a new, empty WeakHashMap with the given initial
* capacity and the given load factor.
*
* @param initialCapacity The initial capacity of the WeakHashMap
* @param loadFactor The load factor of the WeakHashMap
* @throws IllegalArgumentException If the initial capacity is negative,
* or if the load factor is nonpositive.
*/
@SuppressWarnings("unchecked")
public WeakIdentityHashMap(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 = new Entry[capacity];
this.loadFactor = loadFactor;
threshold = (int)(capacity * loadFactor);
}
/**
* Constructs a new, empty WeakHashMap with the given initial
* capacity and the default load factor, which is 0.75.
*
* @param initialCapacity The initial capacity of the WeakHashMap
* @throws IllegalArgumentException If the initial capacity is negative.
*/
public WeakIdentityHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs a new, empty WeakHashMap with the default initial
* capacity (16) and the default load factor (0.75).
*/
@SuppressWarnings("unchecked")
public WeakIdentityHashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR;
threshold = DEFAULT_INITIAL_CAPACITY;
table = new Entry[DEFAULT_INITIAL_CAPACITY];
}
/**
* Constructs a new WeakHashMap with the same mappings as the
* specified Map. The WeakHashMap is created with
* default load factor, which is 0.75 and an initial capacity
* sufficient to hold the mappings in the specified Map.
*
* @param t the map whose mappings are to be placed in this map.
* @throws NullPointerException if the specified map is null.
* @since 1.3
*/
public WeakIdentityHashMap(Map t) {
this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1, 16),
DEFAULT_LOAD_FACTOR);
putAll(t);
}
// 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.
*/
@SuppressWarnings("unchecked")
private static K maskNull(Object key) {
return (K) (key == null ? NULL_KEY : key);
}
/**
* Return internal representation of null key back to caller as null.
*/
@SuppressWarnings("unchecked")
private static K unmaskNull(Object key) {
return (K) (key == NULL_KEY ? null : key);
}
/**
* Return index for hash code h.
*/
private static int indexFor(int h, int length) {
return h & (length-1);
}
/**
* Expunge stale entries from the table.
*/
@SuppressWarnings("unchecked")
private void expungeStaleEntries() {
Entry e;
while ( (e = (Entry) queue.poll()) != null) {
int h = e.hash;
int i = indexFor(h, table.length);
Entry prev = table[i];
Entry p = prev;
while (p != null) {
Entry next = p.next;
if (p == e) {
if (prev == e)
table[i] = next;
else
prev.next = next;
e.next = null; // Help GC
e.value = null; // " "
size--;
break;
}
prev = p;
p = next;
}
}
}
/**
* Return the table after first expunging stale entries
*/
private Entry[] getTable() {
expungeStaleEntries();
return table;
}
/**
* Returns the number of key-value mappings in this map.
* This result is a snapshot, and may not reflect unprocessed
* entries that will be removed before next attempted access
* because they are no longer referenced.
*/
public int size() {
if (size == 0)
return 0;
expungeStaleEntries();
return size;
}
/**
* Returns true if this map contains no key-value mappings.
* This result is a snapshot, and may not reflect unprocessed
* entries that will be removed before next attempted access
* because they are no longer referenced.
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Returns the value to which the specified key is mapped in this weak
* hash map, or null if the map contains no mapping for
* this key. A return value of null does not necessarily
* indicate that the map contains no mapping for the key; it is also
* possible that the map explicitly maps the key to null. The
* containsKey method may be used to distinguish these two
* cases.
*
* @param key the key whose associated value is to be returned.
* @return the value to which this map maps the specified key, or
* null if the map contains no mapping for this key.
* @see #put(Object, Object)
*/
public V get(Object key) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int index = indexFor(h, tab.length);
Entry e = tab[index];
while (e != null) {
if (e.hash == h && k == e.get())
return e.value;
e = e.next;
}
return null;
}
/**
* Returns true if this map contains a mapping for the
* specified key.
*
* @param key The key whose presence in this map is to be tested
* @return true if there is a mapping for key;
* false otherwise
*/
public boolean containsKey(Object key) {
return getEntry(key) != null;
}
/**
* Returns the entry associated with the specified key in the HashMap.
* Returns null if the HashMap contains no mapping for this key.
*/
private Entry getEntry(Object key) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int index = indexFor(h, tab.length);
Entry e = tab[index];
while (e != null && !(e.hash == h && 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 previous value associated with specified key, or null
* if there was no mapping for key. A null return can
* also indicate that the HashMap previously associated
* null with the specified key.
*/
@SuppressWarnings("unchecked")
public V put(K key, V value) {
K k = (K) maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int i = indexFor(h, tab.length);
for (Entry e = tab[i]; e != null; e = e.next) {
if (h == e.hash && k == e.get()) {
V oldValue = e.value;
if (value != oldValue)
e.value = value;
return oldValue;
}
}
modCount++;
Entry e = tab[i];
tab[i] = new Entry(k, value, queue, h, e);
if (++size >= threshold)
resize(tab.length * 2);
return null;
}
/**
* Rehashes the contents of this map into a new array with a
* larger capacity. This method is called automatically when the
* number of keys in this map reaches its threshold.
*
* If current capacity is MAXIMUM_CAPACITY, this method does not
* resize the map, but sets threshold to Integer.MAX_VALUE.
* This has the effect of preventing future calls.
*
* @param newCapacity the new capacity, MUST be a power of two;
* must be greater than current capacity unless current
* capacity is MAXIMUM_CAPACITY (in which case value
* is irrelevant).
*/
@SuppressWarnings("unchecked")
private void resize(int newCapacity) {
Entry[] oldTable = getTable();
int oldCapacity = oldTable.length;
if (oldCapacity == MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return;
}
Entry[] newTable = new Entry[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;
}
}
/** Transfer all entries from src to dest tables */
private void transfer(Entry[] src, Entry[] dest) {
for (int j = 0; j < src.length; ++j) {
Entry e = src[j];
src[j] = null;
while (e != null) {
Entry next = e.next;
Object key = e.get();
if (key == null) {
e.next = null; // Help GC
e.value = null; // " "
size--;
} else {
int i = indexFor(e.hash, dest.length);
e.next = dest[i];
dest[i] = e;
}
e = next;
}
}
}
/**
* Copies all of the mappings from the specified map to this map These
* mappings will replace any mappings that this map had for any of the
* keys currently in the specified map.
*
* @param m mappings to be stored in this map.
* @throws NullPointerException if the specified map is null.
*/
public void putAll(Map m) {
int numKeysToBeAdded = m.size();
if (numKeysToBeAdded == 0)
return;
/*
* Expand the map if the map if the number of mappings to be added
* is greater than or equal to threshold. This is conservative; the
* obvious condition is (m.size() + size) >= threshold, but this
* condition could result in a map with twice the appropriate capacity,
* if the keys to be added overlap with the keys already in this map.
* By using the conservative calculation, we subject ourself
* to at most one extra resize.
*/
if (numKeysToBeAdded > threshold) {
int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
if (targetCapacity > MAXIMUM_CAPACITY)
targetCapacity = MAXIMUM_CAPACITY;
int newCapacity = table.length;
while (newCapacity < targetCapacity)
newCapacity <<= 1;
if (newCapacity > table.length)
resize(newCapacity);
}
for (Iterator> i = m.entrySet().iterator(); i.hasNext(); ) {
Map.Entry e = i.next();
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 previous value associated with specified key, or null
* if there was no mapping for key. A null return can
* also indicate that the map previously associated null
* with the specified key.
*/
public V remove(Object key) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int i = indexFor(h, tab.length);
Entry prev = tab[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (h == e.hash && 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 */
@SuppressWarnings("unchecked")
private Entry removeMapping(Object o) {
if (!(o instanceof Map.Entry))
return null;
Entry[] tab = getTable();
Map.Entry entry = (Map.Entry)o;
Object k = maskNull(entry.getKey());
int h = hash(k);
int i = indexFor(h, tab.length);
Entry prev = tab[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (h == e.hash && e.equals(entry)) {
modCount++;
size--;
if (prev == e)
tab[i] = next;
else
prev.next = next;
return e;
}
prev = e;
e = next;
}
return null;
}
/**
* Removes all mappings from this map.
*/
public void clear() {
// clear out ref queue. We don't need to expunge entries
// since table is getting cleared.
while (queue.poll() != null)
{ /** Nothing */ }
modCount++;
Entry[] tab = table;
for (int i = 0; i < tab.length; ++i)
tab[i] = 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)
{ /** Nothing */ }
}
/**
* Returns true if this map maps one or more keys to the
* specified value.
*
* @param value value whose presence in this map is to be tested.
* @return true if this map maps one or more keys to the
* specified value.
*/
public boolean containsValue(Object value) {
if (value==null)
return containsNullValue();
Entry[] tab = getTable();
for (int i = tab.length ; i-- > 0 ;)
for (Entry e = tab[i] ; e != null ; e = e.next)
if (value.equals(e.value))
return true;
return false;
}
/**
* Special-case code for containsValue with null argument
*/
private boolean containsNullValue() {
Entry[] tab = getTable();
for (int i = tab.length ; i-- > 0 ;)
for (Entry e = tab[i] ; e != null ; e = e.next)
if (e.value==null)
return true;
return false;
}
/**
* The entries in this hash table extend WeakReference, using its main ref
* field as the key.
*/
private static class Entry extends WeakReference
implements Map.Entry {
private V value;
private final int hash;
private Entry next;
/**
* Create new entry.
*/
Entry(K key, V value,
ReferenceQueue queue,
int hash, Entry next) {
super(key, queue);
this.value = value;
this.hash = hash;
this.next = next;
}
public K getKey() {
return WeakIdentityHashMap.unmaskNull(get());
}
public V getValue() {
return value;
}
public V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
@SuppressWarnings("unchecked")
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
if (this == o) {
return true;
}
Map.Entry e = (Map.Entry)o;
Object k1 = getKey();
Object k2 = e.getKey();
if (k1 == k2) {
Object v1 = getValue();
Object v2 = e.getValue();
if (v1 == v2 || (v1 != null && v1.equals(v2)))
return true;
}
return false;
}
public int hashCode() {
Object k = getKey();
Object v = getValue();
return ( ( k == null ? 0 : System.identityHashCode( k ) ) ^
( v == null ? 0 : v.hashCode() ) );
}
public String toString() {
return getKey() + "=" + getValue();
}
}
private abstract class HashIterator implements Iterator {
int index;
Entry entry = null;
Entry lastReturned = null;
int expectedModCount = modCount;
/**
* Strong reference needed to avoid disappearance of key
* between hasNext and next
*/
Object nextKey = null;
/**
* Strong reference needed to avoid disappearance of key
* between nextEntry() and any use of the entry
*/
Object currentKey = null;
HashIterator() {
index = (size() != 0 ? table.length : 0);
}
public boolean hasNext() {
Entry[] t = table;
while (nextKey == null) {
Entry e = entry;
int i = index;
while (e == null && i > 0)
e = t[--i];
entry = e;
index = i;
if (e == null) {
currentKey = null;
return false;
}
nextKey = e.get(); // hold on to key in strong ref
if (nextKey == null)
entry = entry.next;
}
return true;
}
/** The common parts of next() across different types of iterators */
protected Entry nextEntry() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
if (nextKey == null && !hasNext())
throw new NoSuchElementException();
lastReturned = entry;
entry = entry.next;
currentKey = nextKey;
nextKey = null;
return lastReturned;
}
public void remove() {
if (lastReturned == null)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
WeakIdentityHashMap.this.remove(currentKey);
expectedModCount = modCount;
lastReturned = null;
currentKey = null;
}
}
private class ValueIterator extends HashIterator {
public V next() {
return nextEntry().value;
}
}
private class KeyIterator extends HashIterator {
public K next() {
return nextEntry().getKey();
}
}
private class EntryIterator extends HashIterator> {
public Map.Entry next() {
return nextEntry();
}
}
// Views
private transient Set> entrySet = null;
/**
* Returns a 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. The set supports element removal, which removes the
* corresponding mapping from this map, via the Iterator.remove,
* Set.remove, removeAll, retainAll, and
* clear operations. It does not support the add or
* addAll operations.
*
* @return a set view of the keys contained in this map.
*/
public Set keySet() {
Set ks = keySet;
return (ks != null ? ks : (keySet = new KeySet()));
}
private class KeySet extends AbstractSet {
public Iterator iterator() {
return new KeyIterator();
}
public int size() {
return WeakIdentityHashMap.this.size();
}
public boolean contains(Object o) {
return containsKey(o);
}
public boolean remove(Object o) {
if (containsKey(o)) {
WeakIdentityHashMap.this.remove(o);
return true;
}
return false;
}
public void clear() {
WeakIdentityHashMap.this.clear();
}
public Object[] toArray() {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray();
}
public T[] toArray(T[] a) {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray(a);
}
}
/**
* Returns a 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. The collection supports element
* removal, which removes the corresponding mapping from this map, via the
* Iterator.remove, Collection.remove,
* removeAll, retainAll, and clear operations.
* It does not support the add or addAll operations.
*
* @return a collection view of the values contained in this map.
*/
public Collection values() {
Collection vs = values;
return (vs != null ? vs : (values = new Values()));
}
private class Values extends AbstractCollection {
public Iterator iterator() {
return new ValueIterator();
}
public int size() {
return WeakIdentityHashMap.this.size();
}
public boolean contains(Object o) {
return containsValue(o);
}
public void clear() {
WeakIdentityHashMap.this.clear();
}
public Object[] toArray() {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray();
}
public T[] toArray(T[] a) {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray(a);
}
}
/**
* Returns a collection view of the mappings contained in this map. Each
* element in the returned collection is a Map.Entry. The
* collection is backed by the map, so changes to the map are reflected in
* the collection, and vice-versa. The collection supports element
* removal, which removes the corresponding mapping from the map, via the
* Iterator.remove, Collection.remove,
* removeAll, retainAll, and clear operations.
* It does not support the add or addAll operations.
*
* @return a collection view of the mappings contained in this map.
*/
public Set> entrySet() {
Set> es = entrySet;
return (es != null ? es : (entrySet = new EntrySet()));
}
private class EntrySet extends AbstractSet> {
public Iterator> iterator() {
return new EntryIterator();
}
@SuppressWarnings("unchecked")
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
Entry candidate = getEntry(e.getKey());
return candidate != null && candidate.equals(e);
}
public boolean remove(Object o) {
return removeMapping(o) != null;
}
public int size() {
return WeakIdentityHashMap.this.size();
}
public void clear() {
WeakIdentityHashMap.this.clear();
}
public Object[] toArray() {
Collection> c = new ArrayList>(size());
for (Iterator> i = iterator(); i.hasNext(); )
c.add(new SimpleEntry(i.next()));
return c.toArray();
}
public T[] toArray(T[] a) {
Collection> c = new ArrayList>(size());
for (Iterator> i = iterator(); i.hasNext(); )
c.add(new SimpleEntry(i.next()));
return c.toArray(a);
}
}
//Added by TZ
/**
* Return a hash code for non-null Object x.
*/
private static int hash(Object x) {
int h = System.identityHashCode( x );
return h - ( h << 7 ); // that is -127 * h //copied from JBoss
}
// Views
/**
* Each of these fields are initialized to contain an instance of the
* appropriate view the first time this view is requested. The views are
* stateless, so there's no reason to create more than one of each.
*/
private transient volatile Set keySet = null;
private transient volatile Collection values = null;
/**
* This should be made public as soon as possible. It greatly simplifies
* the task of implementing Map.
*/
static class SimpleEntry implements Map.Entry {
K key;
V value;
SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
SimpleEntry(Map.Entry e) {
this.key = e.getKey();
this.value = e.getValue();
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
@SuppressWarnings("unchecked")
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
if (this == o) {
return true;
}
Map.Entry e = (Map.Entry)o;
return key == e.getKey() &&
(value == e.getValue() || (value != null && value.equals(e.getValue())));
}
public int hashCode() {
return ((key == null) ? 0 : key.hashCode()) ^
((value == null) ? 0 : value.hashCode());
}
public String toString() {
return key + "=" + value;
}
}
}