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com.go.trove.util
Class NullKeyMap  

java.lang.Object
  java.util.AbstractMap
      com.go.trove.util.NullKeyMap

All Implemented Interfaces:

java.util.Map, java.io.Serializable

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public class NullKeyMap

extends java.util.AbstractMap

implements java.io.Serializable

A Map supporting null keys that wraps a Map that doesn't support null keys. NullKeyMap substitutes null keys with a special placeholder object. This technique does not work when the wrapped Map is a TreeMap because it cannot be compared against other objects. In order for TreeMaps to support null keys, use any of the null ordering comparators found in the Utils class.

Version:

9 , 9/07/00

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Nested Class Summary

 

Nested classes inherited from class java.util.AbstractMap

 

Nested classes inherited from class java.util.Map

java.util.Map.Entry

 

Field Summary
private  java.util.Set	mEntrySet
private  java.util.Set	mKeySet
private  java.util.Map	mMap
private static java.lang.Object	NULL

 

Fields inherited from class java.util.AbstractMap

 

Constructor Summary

NullKeyMap(java.util.Map map)

 

Method Summary
void	clear()           Remove all entries from this Map (optional operation).
boolean	containsKey(java.lang.Object key)           Returns true if this contains a mapping for the given key.
boolean	containsValue(java.lang.Object value)           Returns true if this contains at least one mapping with the given value.
java.util.Set	entrySet()           Returns a set view of the mappings in this Map.
java.lang.Object	get(java.lang.Object key)           Returns the value mapped by the given key.
boolean	isEmpty()           Returns true if the map contains no mappings.
java.util.Set	keySet()           Returns a set view of this map's keys.
java.lang.Object	put(java.lang.Object key, java.lang.Object value)           Associates the given key to the given value (optional operation).
void	putAll(java.util.Map map)           Copies all entries of the given map to this one (optional operation).
java.lang.Object	remove(java.lang.Object key)           Removes the mapping for this key if present (optional operation).
int	size()           Returns the number of key-value mappings in the map.
java.util.Collection	values()           Returns a collection or bag view of this map's values.

 

Methods inherited from class java.util.AbstractMap

clone, equals, hashCode, toString

 

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

 

Field Detail

NULL

private static final java.lang.Object NULL

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mMap

private java.util.Map mMap

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mKeySet

private transient java.util.Set mKeySet

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mEntrySet

private transient java.util.Set mEntrySet

Constructor Detail

NullKeyMap

public NullKeyMap(java.util.Map map)

Method Detail

size

public int size()

Description copied from class: java.util.AbstractMap

Returns the number of key-value mappings in the map. If there are more than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE. This is implemented as entrySet().size().

Specified by:

size in interface java.util.Map

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isEmpty

public boolean isEmpty()

Description copied from class: java.util.AbstractMap

Returns true if the map contains no mappings. This is implemented by size() == 0.

Specified by:

isEmpty in interface java.util.Map

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containsKey

public boolean containsKey(java.lang.Object key)

Description copied from class: java.util.AbstractMap

Returns true if this contains a mapping for the given key. This implementation does a linear search, O(n), over the entrySet(), returning true if a match is found, false if the iteration ends. Many subclasses can implement this more efficiently.

Specified by:

containsKey in interface java.util.Map

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containsValue

public boolean containsValue(java.lang.Object value)

Description copied from class: java.util.AbstractMap

Returns true if this contains at least one mapping with the given value. This implementation does a linear search, O(n), over the entrySet(), returning true if a match is found, false if the iteration ends. A match is defined as a value, v, where (value == null ? v == null : value.equals(v)). Subclasses are unlikely to implement this more efficiently.

Specified by:

containsValue in interface java.util.Map

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get

public java.lang.Object get(java.lang.Object key)

Description copied from class: java.util.AbstractMap

Returns the value mapped by the given key. Returns null if there is no mapping. However, in Maps that accept null values, you must rely on containsKey to determine if a mapping exists. This iteration takes linear time, searching entrySet().iterator() of the key. Many implementations override this method.

Specified by:

get in interface java.util.Map

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put

public java.lang.Object put(java.lang.Object key,
                            java.lang.Object value)

Description copied from class: java.util.AbstractMap

Associates the given key to the given value (optional operation). If the map already contains the key, its value is replaced. This implementation simply throws an UnsupportedOperationException. Be aware that in a map that permits null values, a null return does not always imply that the mapping was created.

Specified by:

put in interface java.util.Map

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remove

public java.lang.Object remove(java.lang.Object key)

Description copied from class: java.util.AbstractMap

Removes the mapping for this key if present (optional operation). This implementation iterates over the entrySet searching for a matching key, at which point it calls the iterator's remove method. It returns the result of getValue() on the entry, if found, or null if no entry is found. Note that maps which permit null values may also return null if the key was removed. If the entrySet does not support removal, this will also fail. This is O(n), so many implementations override it for efficiency.

Specified by:

remove in interface java.util.Map

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putAll

public void putAll(java.util.Map map)

Description copied from class: java.util.AbstractMap

Copies all entries of the given map to this one (optional operation). If the map already contains a key, its value is replaced. This implementation simply iterates over the map's entrySet(), calling put, so it is not supported if puts are not.

Specified by:

putAll in interface java.util.Map

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clear

public void clear()

Description copied from class: java.util.AbstractMap

Remove all entries from this Map (optional operation). This default implementation calls entrySet().clear(). NOTE: If the entry set does not permit clearing, then this will fail, too. Subclasses often override this for efficiency. Your implementation of entrySet() should not call AbstractMap.clear unless you want an infinite loop.

Specified by:

clear in interface java.util.Map

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keySet

public java.util.Set keySet()

Description copied from class: java.util.AbstractMap

Returns a set view of this map's keys. The set is backed by the map, so changes in one show up in the other. Modifications while an iteration is in progress produce undefined behavior. The set supports removal if entrySet() does, but does not support element addition.

This implementation creates an AbstractSet, where the iterator wraps the entrySet iterator, size defers to the Map's size, and contains defers to the Map's containsKey. The set is created on first use, and returned on subsequent uses, although since no synchronization occurs, there is a slight possibility of creating two sets.

Specified by:

keySet in interface java.util.Map

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values

public java.util.Collection values()

Description copied from class: java.util.AbstractMap

Returns a collection or bag view of this map's values. The collection is backed by the map, so changes in one show up in the other. Modifications while an iteration is in progress produce undefined behavior. The collection supports removal if entrySet() does, but does not support element addition.

This implementation creates an AbstractCollection, where the iterator wraps the entrySet iterator, size defers to the Map's size, and contains defers to the Map's containsValue. The collection is created on first use, and returned on subsequent uses, although since no synchronization occurs, there is a slight possibility of creating two collections.

Specified by:

values in interface java.util.Map

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entrySet

public java.util.Set entrySet()

Description copied from class: java.util.AbstractMap

Returns a set view of the mappings in this Map. Each element in the set must be an implementation of Map.Entry. The set is backed by the map, so that changes in one show up in the other. Modifications made while an iterator is in progress cause undefined behavior. If the set supports removal, these methods must be valid: Iterator.remove, Set.remove, removeAll, retainAll, and clear. Element addition is not supported via this set.

Specified by:

entrySet in interface java.util.Map

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