Map<K,V> (GNU Classpath 0.94-pre Documentation)

An object that maps keys onto values. Keys cannot be duplicated. This interface replaces the obsolete {@link Dictionary} abstract class.

The map has three collection views, which are backed by the map (modifications on one show up on the other): a set of keys, a collection of values, and a set of key-value mappings. Some maps have a guaranteed order, but not all do.

Note: Be careful about using mutable keys. Behavior is unspecified if a key's comparison behavior is changed after the fact. As a corollary to this rule, don't use a Map as one of its own keys or values, as it makes hashCode and equals have undefined behavior.

All maps are recommended to provide a no argument constructor, which builds an empty map, and one that accepts a Map parameter and copies the mappings (usually by putAll), to create an equivalent map. Unfortunately, Java cannot enforce these suggestions.

The map may be unmodifiable, in which case unsupported operations will throw an UnsupportedOperationException. Note that some operations may be safe, such as putAll(m) where m is empty, even if the operation would normally fail with a non-empty argument.

Since: 1.2

UNKNOWN: updated to 1.4

Nested Class Summary
static interface	Map.Entry<K,V> A map entry (key-value pair).

Method Summary
void	clear() Remove all entries from this Map (optional operation).
boolean	containsKey(Object key) Returns true if this contains a mapping for the given key.
boolean	containsValue(Object value) Returns true if this contains at least one mapping with the given value.
Set<Entry<K,V>>	entrySet() Returns a set view of the mappings in this Map.
boolean	equals(Object o) Compares the specified object with this map for equality.
V	get(Object key) Returns the value mapped by the given key.
int	hashCode() Returns the hash code for this map.
boolean	isEmpty() Returns true if the map contains no mappings.
Set<K>	keySet() Returns a set view of the keys in this Map.
V	put(K key, V value) Associates the given key to the given value (optional operation).
void	putAll(Map<? extends K,? extends V> m) Copies all entries of the given map to this one (optional operation).
V	remove(Object o) Removes the mapping for this key if present (optional operation).
int	size() Returns the number of key-value mappings in the map.
Collection<V>	values() Returns a collection (or bag) view of the values in this Map.

Method Detail

clear

containsKey

Returns true if this contains a mapping for the given key.

Parameters: key the key to search for

Returns: true if the map contains the key

Throws: ClassCastException if the key is of an inappropriate type NullPointerException if key is null but the map does not permit null keys

containsValue

Returns true if this contains at least one mapping with the given value. In other words, returns true if a value v exists where (value == null ? v == null : value.equals(v)). This usually requires linear time.

Parameters: value the value to search for

Returns: true if the map contains the value

Throws: ClassCastException if the type of the value is not a valid type for this map. NullPointerException if the value is null and the map doesn't support null values.

entrySet

Returns a set view of the mappings in this Map. Each element in the set is a 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 remove the underlying mapping from the map: Iterator.remove, Set.remove, removeAll, retainAll, and clear. Element addition, via add or addAll, is not supported via this set.

Returns: the set view of all mapping entries

Interface Map<K,V>