## org.apache.commons.collections
Class ReferenceMap

    java.lang.Object
      java.util.AbstractMap
          org.apache.commons.collections.ReferenceMap

All Implemented Interfaces:
  Map

Deprecated. Moved to map subpackage. Due to be removed in v4.0.

public class ReferenceMap
extends AbstractMap

Hash-based `Map` implementation that allows mappings to be removed by the garbage collector.

When you construct a `ReferenceMap`, you can specify what kind of references are used to store the map's keys and values. If non-hard references are used, then the garbage collector can remove mappings if a key or value becomes unreachable, or if the JVM's memory is running low. For information on how the different reference types behave, see `Reference`.

Different types of references can be specified for keys and values. The keys can be configured to be weak but the values hard, in which case this class will behave like a `WeakHashMap`. However, you can also specify hard keys and weak values, or any other combination. The default constructor uses hard keys and soft values, providing a memory-sensitive cache.

The algorithms used are basically the same as those in `HashMap`. In particular, you can specify a load factor and capacity to suit your needs. All optional `Map` operations are supported.

However, this `Map` implementation does not allow null elements. Attempting to add a null key or or a null value to the map will raise a `NullPointerException`.

As usual, this implementation is not synchronized. You can use `Collections.synchronizedMap(java.util.Map)` to provide synchronized access to a `ReferenceMap`.

Since:
  Commons Collections 2.1
Version:
  $Revision: 1.22 $ $Date: 2004/02/18 01:15:42 $
Author:
  Paul Jack
See Also:
  `Reference`

Field Summary
`static int` `HARD` Deprecated. Constant indicating that hard references should be used.
`static int` `SOFT` Deprecated. Constant indicating that soft references should be used.
`static int` `WEAK` Deprecated. Constant indicating that weak references should be used.

Constructor Summary
`ReferenceMap()` Deprecated. Constructs a new `ReferenceMap` that will use hard references to keys and soft references to values.
`ReferenceMap(int keyType, int valueType)` Deprecated. Constructs a new `ReferenceMap` that will use the specified types of references.
`ReferenceMap(int keyType, int valueType, boolean purgeValues)` Deprecated. Constructs a new `ReferenceMap` that will use the specified types of references.
`ReferenceMap(int keyType, int valueType, int capacity, float loadFactor)` Deprecated. Constructs a new `ReferenceMap` with the specified reference types, load factor and initial capacity.
`ReferenceMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues)` Deprecated. Constructs a new `ReferenceMap` with the specified reference types, load factor and initial capacity.

Method Summary
`void` `clear()` Deprecated. Clears this map.
`boolean` `containsKey(Object key)` Deprecated. Returns `true` if this map contains the given key.
`Set` `entrySet()` Deprecated. Returns a set view of this map's entries.
`Object` `get(Object key)` Deprecated. Returns the value associated with the given key, if any.
`boolean` `isEmpty()` Deprecated. Returns `true` if this map is empty.
`Set` `keySet()` Deprecated. Returns a set view of this map's keys.
`Object` `put(Object key, Object value)` Deprecated. Associates the given key with the given value.
`Object` `remove(Object key)` Deprecated. Removes the key and its associated value from this map.
`int` `size()` Deprecated. Returns the size of this map.
`Collection` `values()` Deprecated. Returns a collection view of this map's values.

Methods inherited from class java.util.AbstractMap
`clone, containsValue, equals, hashCode, putAll, toString`

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Field Detail

### HARD

    public static final int HARD

  Deprecated.
  Constant indicating that hard references should be used.

  See Also:
    Constant Field Values

### SOFT

    public static final int SOFT

  Deprecated.
  Constant indicating that soft references should be used.

  See Also:
    Constant Field Values

### WEAK

    public static final int WEAK

  Deprecated.
  Constant indicating that weak references should be used.

  See Also:
    Constant Field Values

Constructor Detail

### ReferenceMap

    public ReferenceMap()

  Deprecated.
  Constructs a new `ReferenceMap` that will use hard references to keys and soft references to values.

### ReferenceMap

    public ReferenceMap(int keyType,
                        int valueType,
                        boolean purgeValues)

  Deprecated.
  Constructs a new `ReferenceMap` that will use the specified types of references.

Parameters:
  `keyType` - the type of reference to use for keys; must be `HARD`, `SOFT`, `WEAK`
  `valueType` - the type of reference to use for values; must be `HARD`, `SOFT`, `WEAK`
  `purgeValues` - should the value be automatically purged when the key is garbage collected

### ReferenceMap

    public ReferenceMap(int keyType,
                        int valueType)

  Deprecated.
  Constructs a new `ReferenceMap` that will use the specified types of references.

Parameters:
  `keyType` - the type of reference to use for keys; must be `HARD`, `SOFT`, `WEAK`
  `valueType` - the type of reference to use for values; must be `HARD`, `SOFT`, `WEAK`

### ReferenceMap

    public ReferenceMap(int keyType,
                        int valueType,
                        int capacity,
                        float loadFactor,
                        boolean purgeValues)

  Deprecated.
  Constructs a new `ReferenceMap` with the specified reference types, load factor and initial capacity.

Parameters:
  `keyType` - the type of reference to use for keys; must be `HARD`, `SOFT`, `WEAK`
  `valueType` - the type of reference to use for values; must be `HARD`, `SOFT`, `WEAK`
  `capacity` - the initial capacity for the map
  `loadFactor` - the load factor for the map
  `purgeValues` - should the value be automatically purged when the key is garbage collected

### ReferenceMap

    public ReferenceMap(int keyType,
                        int valueType,
                        int capacity,
                        float loadFactor)

  Deprecated.
  Constructs a new `ReferenceMap` with the specified reference types, load factor and initial capacity.

Parameters:
  `keyType` - the type of reference to use for keys; must be `HARD`, `SOFT`, `WEAK`
  `valueType` - the type of reference to use for values; must be `HARD`, `SOFT`, `WEAK`
  `capacity` - the initial capacity for the map
  `loadFactor` - the load factor for the map

Method Detail

### size

    public int size()

  Deprecated.
  Returns the size of this map.

  Returns:
    the size of this map

### isEmpty

    public boolean isEmpty()

  Deprecated.
  Returns `true` if this map is empty.

  Returns:
    `true` if this map is empty

### containsKey

    public boolean containsKey(Object key)

  Deprecated.
  Returns `true` if this map contains the given key.

  Returns:
    true if the given key is in this map

### get

    public Object get(Object key)

  Deprecated.
  Returns the value associated with the given key, if any.

  Returns:
    the value associated with the given key, or `null` if the key maps to no value

### put

    public Object put(Object key,
                      Object value)

  Deprecated.
  Associates the given key with the given value.

  Neither the key nor the value may be null.

  Parameters:
    `key` - the key of the mapping
    `value` - the value of the mapping
  Returns:
    the last value associated with that key, or null if no value was associated with the key
  Throws:
    `NullPointerException` - if either the key or value is null

### remove

    public Object remove(Object key)

  Deprecated.
  Removes the key and its associated value from this map.

  Parameters:
    `key` - the key to remove
  Returns:
    the value associated with that key, or null if the key was not in the map

### clear

    public void clear()

  Deprecated.
  Clears this map.

### entrySet

    public Set entrySet()

  Deprecated.
  Returns a set view of this map's entries.

  Returns:
    a set view of this map's entries

### keySet

    public Set keySet()

  Deprecated.
  Returns a set view of this map's keys.

  Returns:
    a set view of this map's keys

### values

    public Collection values()

  Deprecated.
  Returns a collection view of this map's values.

  Returns:
    a collection view of this map's values.

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