com.go.trove.util
Class IdentityMap

java.lang.Object
  |
  +--java.util.AbstractMap
        |
        +--com.go.trove.util.IdentityMap
All Implemented Interfaces:
java.lang.Cloneable, java.util.Map

public class IdentityMap
extends java.util.AbstractMap
implements java.util.Map, java.lang.Cloneable

An IdentityMap is like WeakHashMap, except it uses a key's identity hashcode and equals methods. IdentityMap is not thread-safe and must be wrapped with Collections.synchronizedMap to be made thread-safe. Most of the implementation for this class is ripped off from java.util.HashMap, but not java.util.WeakHashMap, in order to acheive greater efficiency.

The documentation for WeakHashMap states that it is intended primarily for use with key objects whose equals methods test for object identity using the == operator. Because WeakHashMap uses a key's own equals and hashcode methods, it is better suited for implementing methods that behave like String.intern(). However, because WeakHashMap stongly references values, Utils.intern provides a safer intern mechanism.

In this implementation, all key objects are tested for equality using the == operator, and null keys are not permitted. IdentityMap is therefore better suited for "canonicalized" mappings.

Note: Weakly referenced entries may be automatically removed during either accessor or mutator operations, possibly causing a concurrent modification to be detected. Therefore, even if multiple threads are only accessing this map, be sure to synchronize this map first. Also, do not rely on the value returned by size() when using an iterator from this map. The iterators may return less entries than the amount reported by size().

Version:
19 , 00/12/18
Author:
Brian S O'Neill
See Also:
java.util.WeakHashMap, HashMap

Inner classes inherited from class java.util.Map
java.util.Map.Entry
 
Constructor Summary
IdentityMap()
          Constructs a new, empty map with a default capacity and load factor, which is 0.75.
IdentityMap(int initialCapacity)
          Constructs a new, empty map with the specified initial capacity and default load factor, which is 0.75.
IdentityMap(int initialCapacity, float loadFactor)
          Constructs a new, empty map with the specified initial capacity and the specified load factor.
IdentityMap(java.util.Map t)
          Constructs a new map with the same mappings as the given map.
 
Method Summary
 void clear()
          Removes all mappings from this map.
 java.lang.Object clone()
          Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
 boolean containsKey(java.lang.Object key)
          Returns true if this map contains a mapping for the specified key.
 boolean containsValue(java.lang.Object value)
          Returns true if this map maps one or more keys to the specified value.
 java.util.Set entrySet()
          Returns a collection view of the mappings contained in this map.
 java.lang.Object get(java.lang.Object key)
          Returns the value to which this map maps the specified key.
 boolean isEmpty()
          Returns true if this map contains no key-value mappings.
 java.util.Set keySet()
          Returns a set view of the keys contained in this map.
 java.lang.Object put(java.lang.Object key, java.lang.Object value)
          Associates the specified value with the specified key in this map.
 void putAll(java.util.Map t)
          Copies all of the mappings from the specified map to this one.
 java.lang.Object remove(java.lang.Object key)
          Removes the mapping for this key from this map if present.
 int size()
          Returns the number of key-value mappings in this map, but this value may be larger than actual amount of entries produced by an iterator.
 java.lang.String toString()
           
 java.util.Collection values()
          Returns a collection view of the values contained in this map.
 
Methods inherited from class java.util.AbstractMap
equals, hashCode
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface java.util.Map
equals, hashCode
 

Constructor Detail

IdentityMap

public IdentityMap(int initialCapacity,
                   float loadFactor)
Constructs a new, empty map with the specified initial capacity and the specified load factor.
Parameters:
initialCapacity - the initial capacity of the HashMap.
loadFactor - the load factor of the HashMap
Throws:
java.lang.IllegalArgumentException - if the initial capacity is less than zero, or if the load factor is nonpositive.

IdentityMap

public IdentityMap(int initialCapacity)
Constructs a new, empty map with the specified initial capacity and default load factor, which is 0.75.
Parameters:
initialCapacity - the initial capacity of the HashMap.
Throws:
java.lang.IllegalArgumentException - if the initial capacity is less than zero.

IdentityMap

public IdentityMap()
Constructs a new, empty map with a default capacity and load factor, which is 0.75.

IdentityMap

public IdentityMap(java.util.Map t)
Constructs a new map with the same mappings as the given map. The map is created with a capacity of twice the number of mappings in the given map or 11 (whichever is greater), and a default load factor, which is 0.75.
Method Detail

size

public int size()
Returns the number of key-value mappings in this map, but this value may be larger than actual amount of entries produced by an iterator.
Specified by:
size in interface java.util.Map
Overrides:
size in class java.util.AbstractMap
Returns:
the number of key-value mappings in this map.

isEmpty

public boolean isEmpty()
Returns true if this map contains no key-value mappings.
Specified by:
isEmpty in interface java.util.Map
Overrides:
isEmpty in class java.util.AbstractMap
Returns:
true if this map contains no key-value mappings.

containsValue

public boolean containsValue(java.lang.Object value)
Returns true if this map maps one or more keys to the specified value.
Specified by:
containsValue in interface java.util.Map
Overrides:
containsValue in class java.util.AbstractMap
Parameters:
value - value whose presence in this map is to be tested.
Returns:
true if this map maps one or more keys to the specified value.

containsKey

public boolean containsKey(java.lang.Object key)
Returns true if this map contains a mapping for the specified key.
Specified by:
containsKey in interface java.util.Map
Overrides:
containsKey in class java.util.AbstractMap
Parameters:
key - key whose presence in this Map is to be tested.
Returns:
true if this map contains a mapping for the specified key.

get

public java.lang.Object get(java.lang.Object key)
Returns the value to which this map maps the specified key. Returns 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's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.
Specified by:
get in interface java.util.Map
Overrides:
get in class java.util.AbstractMap
Parameters:
key - key whose associated value is to be returned.
Returns:
the value to which this map maps the specified key.

put

public java.lang.Object put(java.lang.Object key,
                            java.lang.Object 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.
Specified by:
put in interface java.util.Map
Overrides:
put in class java.util.AbstractMap
Parameters:
key - key with which the specified value is to be associated.
value - value to be associated with the specified key.
Returns:
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.

remove

public java.lang.Object remove(java.lang.Object key)
Removes the mapping for this key from this map if present.
Specified by:
remove in interface java.util.Map
Overrides:
remove in class java.util.AbstractMap
Parameters:
key - key whose mapping is to be removed from the map.
Returns:
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.

putAll

public void putAll(java.util.Map t)
Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified Map.
Specified by:
putAll in interface java.util.Map
Overrides:
putAll in class java.util.AbstractMap
Parameters:
t - Mappings to be stored in this map.

clear

public void clear()
Removes all mappings from this map.
Specified by:
clear in interface java.util.Map
Overrides:
clear in class java.util.AbstractMap

clone

public java.lang.Object clone()
Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
Overrides:
clone in class java.lang.Object
Returns:
a shallow copy of this map.

keySet

public java.util.Set keySet()
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.
Specified by:
keySet in interface java.util.Map
Overrides:
keySet in class java.util.AbstractMap
Returns:
a set view of the keys contained in this map.

values

public java.util.Collection values()
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.
Specified by:
values in interface java.util.Map
Overrides:
values in class java.util.AbstractMap
Returns:
a collection view of the values contained in this map.

entrySet

public java.util.Set entrySet()
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.
Specified by:
entrySet in interface java.util.Map
Overrides:
entrySet in class java.util.AbstractMap
Returns:
a collection view of the mappings contained in this map.
See Also:
Map.Entry

toString

public java.lang.String toString()
Overrides:
toString in class java.util.AbstractMap