## org.apache.lucene.util
Class WeakIdentityMap<K,V>

    java.lang.Object
      org.apache.lucene.util.WeakIdentityMap<K,V>

    public final class WeakIdentityMap<K,V>

extends Object

Implements a combination of `WeakHashMap` and `IdentityHashMap`. Useful for caches that need to key off of a `==` comparison instead of a `.equals`.

This class is not a general-purpose `Map` implementation! It intentionally violates Map's general contract, which mandates the use of the equals method when comparing objects. This class is designed for use only in the rare cases wherein reference-equality semantics are required.

This implementation was forked from Apache CXF but modified to not implement the `Map` interface and without any set views on it, as those are error-prone and inefficient, if not implemented carefully. The map only contains `Iterator` implementations on the values and not-GCed keys. Lucene's implementation also supports `null` keys, but those are never weak!

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Method Summary
`void` `clear()` Removes all of the mappings from this map.
`boolean` `containsKey(Object key)` Returns `true` if this map contains a mapping for the specified key.
`V` `get(Object key)` Returns the value to which the specified key is mapped.
`boolean` `isEmpty()` Returns `true` if this map contains no key-value mappings.
`Iterator<K>` `keyIterator()` Returns an iterator over all weak keys of this map.

`static

`<K,V> WeakIdentityMap<K,V>`

`

`newConcurrentHashMap()`
Creates a new `WeakIdentityMap` based on a `ConcurrentHashMap`.

`static

`<K,V> WeakIdentityMap<K,V>`

`

`newHashMap()`
Creates a new `WeakIdentityMap` based on a non-synchronized `HashMap`.

`V` `put(K key, V value)` Associates the specified value with the specified key in this map.
`V` `remove(Object key)` Removes the mapping for a key from this weak hash map if it is present.
`int` `size()` Returns the number of key-value mappings in this map.
`Iterator<V>` `valueIterator()` Returns an iterator over all values of this map.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Method Detail

### newHashMap

    public static final <K,V> WeakIdentityMap<K,V> newHashMap()

  Creates a new `WeakIdentityMap` based on a non-synchronized `HashMap`.

### newConcurrentHashMap

    public static final <K,V> WeakIdentityMap<K,V> newConcurrentHashMap()

  Creates a new `WeakIdentityMap` based on a `ConcurrentHashMap`.

### clear

    public void clear()

  Removes all of the mappings from this map.

### containsKey

    public boolean containsKey(Object key)

  Returns `true` if this map contains a mapping for the specified key.

### get

    public V get(Object key)

  Returns the value to which the specified key is mapped.

### put

    public V put(K key,
                 V value)

  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.

### isEmpty

    public boolean isEmpty()

  Returns `true` if this map contains no key-value mappings.

### remove

    public V remove(Object key)

  Removes the mapping for a key from this weak hash map if it is present. Returns the value to which this map previously associated the key, or `null` if the map contained no mapping for the key. A return value of `null` does not necessarily indicate that the map contained.

### size

    public int size()

  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.

### keyIterator

    public Iterator<K> keyIterator()

  Returns an iterator over all weak keys of this map. Keys already garbage collected will not be returned. This Iterator does not support removals.

### valueIterator

    public Iterator<V> valueIterator()

  Returns an iterator over all values of this map. This iterator may return values whose key is already garbage collected while iterator is consumed.

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