This documentation differs from the official API. Jadeite adds extra features to the API including: variable font sizes, constructions examples, placeholders for classes and methods, and auto-generated “See Also” links. Additionally it is missing some items found in standard Javadoc documentation, including: generics type information, “Deprecated” tags and comments, “See Also” links, along with other minor differences. Please send any questions or feedback to bam@cs.cmu.edu.


java.util
class AbstractMap

java.lang.Object extended by java.util.AbstractMap
All Implemented Interfaces:
Map
Direct Known Subclasses:
ConcurrentHashMap, ConcurrentSkipListMap, EnumMap, HashMap, IdentityHashMap, TreeMap, WeakHashMap

public abstract class AbstractMap
extends Object
implements Map

This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface.

To implement an unmodifiable map, the programmer needs only to extend this class and provide an implementation for the entrySet method, which returns a set-view of the map's mappings. Typically, the returned set will, in turn, be implemented atop AbstractSet. This set should not support the add or remove methods, and its iterator should not support the remove method.

To implement a modifiable map, the programmer must additionally override this class's put method (which otherwise throws an UnsupportedOperationException), and the iterator returned by entrySet().iterator() must additionally implement its remove method.

The programmer should generally provide a void (no argument) and map constructor, as per the recommendation in the Map interface specification.

The documentation for each non-abstract method in this class describes its implementation in detail. Each of these methods may be overridden if the map being implemented admits a more efficient implementation.

This class is a member of the Java Collections Framework.


Nested Class Summary
static class

           An Entry maintaining a key and a value.
static class

           An Entry maintaining an immutable key and value.
 
Constructor Summary
protected

          Sole constructor.
 
Method Summary
 void

          
protected Object

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

          
 boolean

          
abstract Set

          
 boolean

          Compares the specified object with this map for equality.
 Object
get(Object key)

          
 int

          Returns the hash code value for this map.
 boolean

          
 Set

          
 Object
put(Object key, Object value)

          
 void

          
 Object

          
 int

          
 String

          Returns a string representation of this map.
 Collection

          
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

AbstractMap

protected AbstractMap()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

clear

public void clear()
{@inheritDoc}

This implementation calls entrySet().clear().

Note that this implementation throws an UnsupportedOperationException if the entrySet does not support the clear operation.


clone

protected Object clone()
                throws CloneNotSupportedException
Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.

Overrides:
clone in class Object
Returns:
a shallow copy of this map
Throws:
CloneNotSupportedException

containsKey

public boolean containsKey(Object key)
{@inheritDoc}

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Parameters:
key

containsValue

public boolean containsValue(Object value)
{@inheritDoc}

This implementation iterates over entrySet() searching for an entry with the specified value. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map.

Parameters:
value

entrySet

public abstract Set entrySet()

equals

public boolean equals(Object o)
Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.

This implementation first checks if the specified object is this map; if so it returns true. Then, it checks if the specified object is a map whose size is identical to the size of this map; if not, it returns false. If so, it iterates over this map's entrySet collection, and checks that the specified map contains each mapping that this map contains. If the specified map fails to contain such a mapping, false is returned. If the iteration completes, true is returned.

Overrides:
equals in class Object
Parameters:
o - object to be compared for equality with this map
Returns:
true if the specified object is equal to this map

get

public Object get(Object key)
{@inheritDoc}

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, the entry's value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Parameters:
key

hashCode

public int hashCode()
Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's entrySet() view. This ensures that m1.equals(m2) implies that m1.hashCode()==m2.hashCode() for any two maps m1 and m2, as required by the general contract of {@link Object#hashCode}.

This implementation iterates over entrySet(), calling {@link Map.Entry#hashCode hashCode()} on each element (entry) in the set, and adding up the results.

Overrides:
hashCode in class Object
Returns:
the hash code value for this map

isEmpty

public boolean isEmpty()
{@inheritDoc}

This implementation returns size() == 0.


keySet

public Set keySet()
{@inheritDoc}

This implementation returns a set that subclasses {@link AbstractSet}. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsKey method.

The set is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same set.


put

public Object put(Object key,
                  Object value)
{@inheritDoc}

This implementation always throws an UnsupportedOperationException.

Parameters:
key
value

putAll

public void putAll(Map m)
{@inheritDoc}

This implementation iterates over the specified map's entrySet() collection, and calls this map's put operation once for each entry returned by the iteration.

Note that this implementation throws an UnsupportedOperationException if this map does not support the put operation and the specified map is nonempty.

Parameters:
m

remove

public Object remove(Object key)
{@inheritDoc}

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, its value is obtained with its getValue operation, the entry is removed from the collection (and the backing map) with the iterator's remove operation, and the saved value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Note that this implementation throws an UnsupportedOperationException if the entrySet iterator does not support the remove method and this map contains a mapping for the specified key.

Parameters:
key

size

public int size()
{@inheritDoc}

This implementation returns entrySet().size().


toString

public String toString()
Returns a string representation of this map. The string representation consists of a list of key-value mappings in the order returned by the map's entrySet view's iterator, enclosed in braces ("{}"). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign ("=") followed by the associated value. Keys and values are converted to strings as by {@link String#valueOf(Object)}.

Overrides:
toString in class Object
Returns:
a string representation of this map

values

public Collection values()
{@inheritDoc}

This implementation returns a collection that subclasses {@link AbstractCollection}. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsValue method.

The collection is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same collection.



This documentation differs from the official API. Jadeite adds extra features to the API including: variable font sizes, constructions examples, placeholders for classes and methods, and auto-generated “See Also” links. Additionally it is missing some items found in standard Javadoc documentation, including: generics type information, “Deprecated” tags and comments, “See Also” links, along with other minor differences. Please send any questions or feedback to bam@cs.cmu.edu.
This page displays the Jadeite version of the documention, which is derived from the offical documentation that contains this copyright notice:
Copyright 2008 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
The official Sun™ documentation can be found here at http://java.sun.com/javase/6/docs/api/.