java.util

Class AbstractMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

All Implemented Interfaces:

Map<K,V>

Direct Known Subclasses:

HashMap, IdentityHashMap, TreeMap

public abstract class AbstractMap<K,V>
extends Object
implements Map<K,V>

This class is an abstract implementation of the Map interface. This implementation does not support adding. A subclass must implement the abstract method entrySet().

Since:

1.2

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	AbstractMap.SimpleEntry<K,V> A key-value mapping.
static class	AbstractMap.SimpleImmutableEntry<K,V> An immutable key-value mapping.

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractMap() Constructs a new instance of this AbstractMap.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all elements from this map, leaving it empty.
boolean	containsKey(Object key) Returns whether this map contains the specified key.
boolean	containsValue(Object value) Returns whether this map contains the specified value.
abstract Set<Map.Entry<K,V>>	entrySet() Returns a set containing all of the mappings in this map.
boolean	equals(Object object) Compares the specified object to this instance, and returns true if the specified object is a map and both maps contain the same mappings.
V	get(Object key) Returns the value of the mapping with the specified key.
int	hashCode() Returns the hash code for this object.
boolean	isEmpty() Returns whether this map is empty.
Set<K>	keySet() Returns a set of the keys contained in this map.
V	put(K key, V value) Maps the specified key to the specified value.
void	putAll(Map<? extends K,? extends V> map) Copies every mapping in the specified map to this map.
V	remove(Object key) Removes a mapping with the specified key from this Map.
int	size() Returns the number of elements in this map.
String	toString() Returns the string representation of this map.
Collection<V>	values() Returns a collection of the values contained in this map.

Methods inherited from class java.lang.Object

clone, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

AbstractMap

protected AbstractMap()

Constructs a new instance of this AbstractMap.

Method Detail

clear

public void clear()

Removes all elements from this map, leaving it empty.

Specified by:

clear in interface Map<K,V>

Throws:

UnsupportedOperationException - if removing from this map is not supported.

See Also:

isEmpty(), size()

containsKey

public boolean containsKey(Object key)

Returns whether this map contains the specified key.

Specified by:

containsKey in interface Map<K,V>

Parameters:

key - the key to search for.

Returns:

true if this map contains the specified key, false otherwise.

containsValue

public boolean containsValue(Object value)

Returns whether this map contains the specified value.

Specified by:

containsValue in interface Map<K,V>

Parameters:

value - the value to search for.

Returns:

true if this map contains the specified value, false otherwise.

entrySet

public abstract Set<Map.Entry<K,V>> entrySet()

Returns a set containing all of the mappings in this map. Each mapping is an instance of Map.Entry. As the set is backed by this map, changes in one will be reflected in the other.

Specified by:

entrySet in interface Map<K,V>

Returns:

a set of the mappings.

equals

public boolean equals(Object object)

Compares the specified object to this instance, and returns true if the specified object is a map and both maps contain the same mappings.

Specified by:

equals in interface Map<K,V>

Overrides:

equals in class Object

Parameters:

object - the object to compare with this object.

Returns:

boolean true if the object is the same as this object, and false if it is different from this object.

See Also:

hashCode(), entrySet()

get

public V get(Object key)

Returns the value of the mapping with the specified key.

Specified by:

get in interface Map<K,V>

Parameters:

key - the key.

Returns:

the value of the mapping with the specified key, or null if no mapping for the specified key is found.

hashCode

public int hashCode()

Returns the hash code for this object. Objects which are equal must return the same value for this method.

Specified by:

hashCode in interface Map<K,V>

Overrides:

hashCode in class Object

Returns:

the hash code of this object.

See Also:

equals(Object)

isEmpty

public boolean isEmpty()

Returns whether this map is empty.

Specified by:

isEmpty in interface Map<K,V>

Returns:

true if this map has no elements, false otherwise.

See Also:

size()

keySet

public Set<K> keySet()

Returns a set of the keys contained in this map. The set is backed by this map so changes to one are reflected by the other. The returned set does not support adding.

Specified by:

keySet in interface Map<K,V>

Returns:

a set of the keys.

put

public V put(K key,
             V value)

Maps the specified key to the specified value.

Specified by:

put in interface Map<K,V>

Parameters:

key - the key.

value - the value.

Returns:

the value of any previous mapping with the specified key or null if there was no mapping.

Throws:

UnsupportedOperationException - if adding to this map is not supported.

ClassCastException - if the class of the key or value is inappropriate for this map.

IllegalArgumentException - if the key or value cannot be added to this map.

NullPointerException - if the key or value is null and this Map does not support null keys or values.

putAll

public void putAll(Map<? extends K,? extends V> map)

Copies every mapping in the specified map to this map.

Specified by:

putAll in interface Map<K,V>

Parameters:

map - the map to copy mappings from.

Throws:

UnsupportedOperationException - if adding to this map is not supported.

ClassCastException - if the class of a key or value is inappropriate for this map.

IllegalArgumentException - if a key or value cannot be added to this map.

NullPointerException - if a key or value is null and this map does not support null keys or values.

remove

public V remove(Object key)

Removes a mapping with the specified key from this Map.

Specified by:

remove in interface Map<K,V>

Parameters:

key - the key of the mapping to remove.

Returns:

the value of the removed mapping or null if no mapping for the specified key was found.

Throws:

UnsupportedOperationException - if removing from this map is not supported.

size

public int size()

Returns the number of elements in this map.

Specified by:

size in interface Map<K,V>

Returns:

the number of elements in this map.

toString

public String toString()

Returns the string representation of this map.

Overrides:

toString in class Object

Returns:

the string representation of this map.

values

public Collection<V> values()

Returns a collection of the values contained in this map. The collection is backed by this map so changes to one are reflected by the other. The collection supports remove, removeAll, retainAll and clear operations, and it does not support add or addAll operations.

This method returns a collection which is the subclass of AbstractCollection. The iterator method of this subclass returns a "wrapper object" over the iterator of map's entrySet(). The size method wraps the map's size method and the contains method wraps the map's containsValue method.

The collection is created when this method is called for the first time and returned in response to all subsequent calls. This method may return different collections when multiple concurrent calls occur to this method, since no synchronization is performed.

Specified by:

values in interface Map<K,V>

Returns:

a collection of the values contained in this map.