net.sf.beanlib.util
Class AbstractMap<K,V>

java.lang.Object
  net.sf.beanlib.util.AbstractMap<K,V>

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Implemented Interfaces:

Map<K,V>

Direct Known Subclasses:

ConcurrentSkipListMap, ConcurrentSkipListMap.SubMap

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

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 methods 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.

Since:

1.2

Version:

1.47, 11/17/05

Author:

Josh Bloch, Neal Gafter

See Also:

Map, Collection

Nested Class Summary

static class	AbstractMap.SimpleEntry<K,V> An Entry maintaining a key and a value.
static class	AbstractMap.SimpleImmutableEntry<K,V> An Entry maintaining an immutable key and value.

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

Map.Entry<K,V>

Field Summary

(package private) Set<K>	keySet Each of these fields are initialized to contain an instance of the appropriate view the first time this view is requested.
(package private) Collection<V>	values

Constructor Summary

protected

AbstractMap() Sole constructor.

Method Summary

void	clear()
protected Object	clone() Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.
boolean	containsKey(Object key)
boolean	containsValue(Object value)
abstract Set<Map.Entry<K,V>>	entrySet()
private static boolean	eq(Object o1, Object o2) Utility method for SimpleEntry and SimpleImmutableEntry.
boolean	equals(Object o) Compares the specified object with this map for equality.
V	get(Object key)
int	hashCode() Returns the hash code value for this map.
boolean	isEmpty()
Set<K>	keySet()
V	put(K key, V value)
void	putAll(Map<? extends K,? extends V> m)
V	remove(Object key)
int	size()
String	toString() Returns a string representation of this map.
Collection<V>	values()

Methods inherited from class java.lang.Object

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

Field Detail

keySet

transient volatile Set<K> keySet

Each of these fields are initialized to contain an instance of the appropriate view the first time this view is requested. The views are stateless, so there's no reason to create more than one of each.

values

transient volatile Collection<V> values

Constructor Detail

AbstractMap

protected AbstractMap()

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

Method Detail

size

public int size()

This implementation returns entrySet().size().

Specified by:

size in interface Map<K,V>

isEmpty

public boolean isEmpty()

This implementation returns size() == 0.

Specified by:

isEmpty in interface Map<K,V>

containsValue

public boolean containsValue(Object value)

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.

Specified by:

containsValue in interface Map<K,V>

Throws:

ClassCastException

NullPointerException

containsKey

public boolean containsKey(Object key)

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.

Specified by:

containsKey in interface Map<K,V>

Throws:

ClassCastException

NullPointerException

get

public V get(Object key)

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.

Specified by:

get in interface Map<K,V>

Throws:

ClassCastException

NullPointerException

put

public V put(K key,
             V value)

This implementation always throws an UnsupportedOperationException.

Specified by:

put in interface Map<K,V>

Throws:

UnsupportedOperationException

ClassCastException

NullPointerException

IllegalArgumentException

remove

public V remove(Object key)

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.

Specified by:

remove in interface Map<K,V>

Throws:

UnsupportedOperationException

ClassCastException

NullPointerException

putAll

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

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.

Specified by:

putAll in interface Map<K,V>

Throws:

UnsupportedOperationException

ClassCastException

NullPointerException

IllegalArgumentException

clear

public void clear()

This implementation calls entrySet().clear().

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

Specified by:

clear in interface Map<K,V>

Throws:

UnsupportedOperationException

keySet

public Set<K> keySet()

This implementation returns a set that subclasses 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.

Specified by:

keySet in interface Map<K,V>

values

public Collection<V> values()

This implementation returns a collection that subclasses 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.

Specified by:

values in interface Map<K,V>

entrySet

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

Specified by:

entrySet in interface Map<K,V>

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.

Specified by:

equals in interface Map<K,V>

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

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 Object.hashCode().

This implementation iterates over entrySet(), calling hashCode() on each element (entry) in the set, and adding up the results.

Specified by:

hashCode in interface Map<K,V>

Overrides:

hashCode in class Object

Returns:

the hash code value for this map

See Also:

Map.Entry.hashCode(), Object.equals(Object), Set.equals(Object)

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 String.valueOf(Object).

Overrides:

toString in class Object

Returns:

a string representation of this map

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

eq

private static boolean eq(Object o1,
                          Object o2)

Utility method for SimpleEntry and SimpleImmutableEntry. Test for equality, checking for nulls.