org.apache.commons.collections.map

Class CompositeMap

public class CompositeMap extends Object implements Map

Decorates a map of other maps to provide a single unified view.

Changes made to this map will actually be made on the decorated map. Add and remove operations require the use of a pluggable strategy. If no strategy is provided then add and remove are unsupported.

Note that CompositeMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using java.util.Collections#synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since: Commons Collections 3.0

Version: $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $

Author: Brian McCallister

Nested Class Summary
static interfaceCompositeMap.MapMutator
This interface allows definition for all of the indeterminate mutators in a CompositeMap, as well as providing a hook for callbacks on key collisions.
Constructor Summary
CompositeMap()
Create a new, empty, CompositeMap.
CompositeMap(Map one, Map two)
Create a new CompositeMap with two composited Map instances.
CompositeMap(Map one, Map two, CompositeMap.MapMutator mutator)
Create a new CompositeMap with two composited Map instances.
CompositeMap(Map[] composite)
Create a new CompositeMap which composites all of the Map instances in the argument.
CompositeMap(Map[] composite, CompositeMap.MapMutator mutator)
Create a new CompositeMap which composites all of the Map instances in the argument.
Method Summary
voidaddComposited(Map map)
Add an additional Map to the composite.
voidclear()
Calls clear() on all composited Maps.
booleancontainsKey(Object key)
Returns true if this map contains a mapping for the specified key.
booleancontainsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
SetentrySet()
Returns a set view of the mappings contained in this map.
booleanequals(Object obj)
Checks if this Map equals another as per the Map specification.
Objectget(Object key)
Returns the value to which this map maps the specified key.
inthashCode()
Gets a hash code for the Map as per the Map specification.
booleanisEmpty()
Returns true if this map contains no key-value mappings.
SetkeySet()
Returns a set view of the keys contained in this map.
Objectput(Object key, Object value)
Associates the specified value with the specified key in this map (optional operation).
voidputAll(Map map)
Copies all of the mappings from the specified map to this map (optional operation).
Objectremove(Object key)
Removes the mapping for this key from this map if it is present (optional operation).
MapremoveComposited(Map map)
Remove a Map from the composite.
voidsetMutator(CompositeMap.MapMutator mutator)
Specify the MapMutator to be used by mutation operations.
intsize()
Returns the number of key-value mappings in this map.
Collectionvalues()
Returns a collection view of the values contained in this map.

Constructor Detail

CompositeMap

public CompositeMap()
Create a new, empty, CompositeMap.

CompositeMap

public CompositeMap(Map one, Map two)
Create a new CompositeMap with two composited Map instances.

Parameters: one the first Map to be composited two the second Map to be composited

Throws: IllegalArgumentException if there is a key collision

CompositeMap

public CompositeMap(Map one, Map two, CompositeMap.MapMutator mutator)
Create a new CompositeMap with two composited Map instances.

Parameters: one the first Map to be composited two the second Map to be composited mutator MapMutator to be used for mutation operations

CompositeMap

public CompositeMap(Map[] composite)
Create a new CompositeMap which composites all of the Map instances in the argument. It copies the argument array, it does not use it directly.

Parameters: composite the Maps to be composited

Throws: IllegalArgumentException if there is a key collision

CompositeMap

public CompositeMap(Map[] composite, CompositeMap.MapMutator mutator)
Create a new CompositeMap which composites all of the Map instances in the argument. It copies the argument array, it does not use it directly.

Parameters: composite Maps to be composited mutator MapMutator to be used for mutation operations

Method Detail

addComposited

public void addComposited(Map map)
Add an additional Map to the composite.

Parameters: map the Map to be added to the composite

Throws: IllegalArgumentException if there is a key collision and there is no MapMutator set to handle it.

clear

public void clear()
Calls clear() on all composited Maps.

Throws: UnsupportedOperationException if any of the composited Maps do not support clear()

containsKey

public boolean containsKey(Object key)
Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains at a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Parameters: key key whose presence in this map is to be tested.

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

Throws: ClassCastException if the key is of an inappropriate type for this map (optional). NullPointerException if the key is null and this map does not not permit null keys (optional).

containsValue

public boolean containsValue(Object value)
Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.

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.

Throws: ClassCastException if the value is of an inappropriate type for this map (optional). NullPointerException if the value is null and this map does not not permit null values (optional).

entrySet

public Set entrySet()
Returns a set view of the mappings contained in this map. Each element in the returned set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

This implementation returns a CompositeSet which composites the entry sets from all of the composited maps.

Returns: a set view of the mappings contained in this map.

See Also: CompositeSet

equals

public boolean equals(Object obj)
Checks if this Map equals another as per the Map specification.

Parameters: obj the object to compare to

Returns: true if the maps are equal

get

public Object get(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.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

Parameters: key key whose associated value is to be returned.

Returns: the value to which this map maps the specified key, or null if the map contains no mapping for this key.

Throws: ClassCastException if the key is of an inappropriate type for this map (optional). NullPointerException key is null and this map does not not permit null keys (optional).

See Also: containsKey

hashCode

public int hashCode()
Gets a hash code for the Map as per the Map specification.

isEmpty

public boolean isEmpty()
Returns true if this map contains no key-value mappings.

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

keySet

public 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. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

This implementation returns a CompositeSet which composites the key sets from all of the composited maps.

Returns: a set view of the keys contained in this map.

put

public Object put(Object key, Object value)
Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.))

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 map previously associated null with the specified key, if the implementation supports null values.

Throws: UnsupportedOperationException if no MapMutator has been specified ClassCastException if the class of the specified key or value prevents it from being stored in this map. IllegalArgumentException if some aspect of this key or value prevents it from being stored in this map. NullPointerException this map does not permit null keys or values, and the specified key or value is null.

putAll

public void putAll(Map map)
Copies all of the mappings from the specified map to this map (optional operation). The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is unspecified if the specified map is modified while the operation is in progress.

Parameters: map Mappings to be stored in this map.

Throws: UnsupportedOperationException if the putAll method is not supported by this map. ClassCastException if the class of a key or value in the specified map prevents it from being stored in this map. IllegalArgumentException some aspect of a key or value in the specified map prevents it from being stored in this map. NullPointerException the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values.

remove

public Object remove(Object key)
Removes the mapping for this key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

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.

Throws: ClassCastException if the key is of an inappropriate type for the composited map (optional). NullPointerException if the key is null and the composited map does not not permit null keys (optional). UnsupportedOperationException if the remove method is not supported by the composited map containing the key

removeComposited

public Map removeComposited(Map map)
Remove a Map from the composite.

Parameters: map the Map to be removed from the composite

Returns: The removed Map or null if map is not in the composite

setMutator

public void setMutator(CompositeMap.MapMutator mutator)
Specify the MapMutator to be used by mutation operations.

Parameters: mutator the MapMutator to be used for mutation delegation

size

public int size()
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Returns: the number of key-value mappings in this map.

values

public 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. If the map is modified while an iteration over the collection is in progress, the results of the iteration are undefined. 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.

Returns: a collection view of the values contained in this map.

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