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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

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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()>String.intern() 55 . However, because WeakHashMap stongly references values, Utils.intern 55 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

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Nested Class Summary
private static class	IdentityMap.Entry           HashMap collision list entry.
private  class	IdentityMap.HashIterator

 

Nested classes inherited from class java.util.AbstractMap

 

Field Summary
(package private) static java.util.Iterator	cEmptyHashIterator
(package private) static int	ENTRIES
(package private) static int	KEYS
private  int	mCount           The total number of mappings in the hash table.
private  java.util.Set	mEntrySet
private  java.util.Set	mKeySet
private  float	mLoadFactor           The load factor for the hashtable.
private  int	mModCount           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).
private  IdentityMap.Entry[]	mTable           The hash table data.
private  int	mThreshold           The table is rehashed when its size exceeds this threshold.
private  java.util.Collection	mValues
(package private) static int	VALUES

 

Fields inherited from class java.util.AbstractMap

 

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
private  void	cleanup()           Scans the contents of this map, removing all entries that have a cleared weak key.
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.
private  java.util.Iterator	getHashIterator(int type)
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.
private  void	rehash()           Rehashes the contents of this map into a new HashMap instance with a larger capacity.
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()           Returns a String representation of this map.
(package private) static java.lang.String	toString(java.util.Collection c)           Converts a string to a collection without calling size().
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

 

Field Detail

KEYS

static final int KEYS

See Also:

Constant Field Values

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VALUES

static final int VALUES

See Also:

Constant Field Values

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ENTRIES

static final int ENTRIES

See Also:

Constant Field Values

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cEmptyHashIterator

static final java.util.Iterator cEmptyHashIterator

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mTable

private transient IdentityMap.Entry[] mTable

The hash table data.

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mCount

private transient int mCount

The total number of mappings in the hash table.

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mThreshold

private int mThreshold

The table is rehashed when its size exceeds this threshold. (The value of this field is (int)(capacity * loadFactor).)

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mLoadFactor

private float mLoadFactor

The load factor for the hashtable.

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mModCount

private transient int mModCount

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).

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mKeySet

private transient java.util.Set mKeySet

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mEntrySet

private transient java.util.Set mEntrySet

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mValues

private transient java.util.Collection mValues

Constructor Detail

IdentityMap

public IdentityMap(int initialCapacity,
                   float loadFactor)

Constructs a new, empty map with the specified initial capacity and the specified load factor.

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IdentityMap

public IdentityMap(int initialCapacity)

Constructs a new, empty map with the specified initial capacity and default load factor, which is 0.75.

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IdentityMap

public IdentityMap()

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

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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

toString

static java.lang.String toString(java.util.Collection c)

Converts a string to a collection without calling size(). Iterators from this map may return less entries than the amount reported by size().

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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

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isEmpty

public boolean isEmpty()

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

Specified by:

isEmpty in interface java.util.Map

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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

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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

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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

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cleanup

private void cleanup()

Scans the contents of this map, removing all entries that have a cleared weak key.

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rehash

private void rehash()

Rehashes the contents of this map into a new HashMap instance with a larger capacity. This method is called automatically when the number of keys in this map exceeds its capacity and load factor.

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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

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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

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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

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clear

public void clear()

Removes all mappings from this map.

Specified by:

clear in interface java.util.Map

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clone

public java.lang.Object clone()

Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.

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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

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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

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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

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toString

public java.lang.String toString()

Description copied from class: java.util.AbstractMap

Returns a String representation of this map. This is a listing of the map entries (which are specified in Map.Entry as being getKey() + "=" + getValue()), separated by a comma and space (", "), and surrounded by braces ('{' and '}'). This implementation uses a StringBuffer and iterates over the entrySet to build the String. Note that this can fail with an exception if underlying keys or values complete abruptly in toString().

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getHashIterator

private java.util.Iterator getHashIterator(int type)

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