MapK,V

Map<K,V>

java.util

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Java 1.2

collection

This interface represents a collection of mappings, or associations, between key objects and value objects. Hashtables and associative arrays are examples of maps. In Java 5.0 this interface has been made generic. The type variable K represents the type of the keys held by the map and the type variable V represents the type of the values associated with those keys.

The set of key objects in a Map must not have any duplicates; the collection of value objects is under no such constraint. The key objects should usually be immutable objects, or, if they are not, care should be taken that they do not change while in use in a Map . As of Java 1.2, the Map interface replaces the abstract Dictionary class. Although a Map is not a Collection , the Map interface is still considered an integral part, along with Set , List , and others, of the Java collections framework.

You can add a key/value association to a Map with the put( ) method. Use putAll( ) to copy all mappings from one Map to another. Call get( ) to look up the value object associated with a specified key object. Use remove( ) to delete the mapping between a specified key and its value, or use clear( ) to delete all mappings from a Map . size ( ) returns the number of mappings in a Map , and isEmpty( ) tests whether the Map contains no mappings. containsKey( ) tests whether a Map contains the specified key object, and containsValue( ) tests whether it contains the specified value. (For most implementations , containsValue( ) is a much more expensive operation than containsKey( ) , however.) keySet( ) returns a Set of all key objects in the Map . values( ) returns a Collection (not a Set , since it may contain duplicates) of all value objects in the map. entrySet( ) returns a Set of all mappings in a Map . The elements of this returned Set are Map.Entry objects. The collections returned by values( ) , keySet( ) , and entrySet( ) are based on the Map itself, so changes to the Map are reflected in the collections.

An interface cannot specify constructors, but it is conventional that all implementations of Map provide at least two standard constructors: one that takes no arguments and creates an empty map, and a copy constructor that accepts a Map object that specifies the initial contents of the new Map .

Implementations are required to support all methods that query the contents of a Map , but support for methods that modify the contents of a Map is optional. If an implementation does not support a particular method, the implementation of that method simply throws a java.lang.UnsupportedOperationException . See also Collection , Set , List , HashMap , Hashtable , WeakHashMap , SortedMap , and treeMap .

 public interface  Map<K,V>  {  // Nested Types  public interface  Entry<K,V>  ;  // Public Instance Methods  void  clear  ( );        boolean  containsKey  (Object  key  );        boolean  containsValue  (Object  value  );        Set<Map.Entry<K,V>>  entrySet  ( );        boolean  equals  (Object  o  );        V  get  (Object  key  );        int  hashCode  ( );        boolean  isEmpty  ( );        Set<K>  keySet  ( );        V  put  (K  key  , V  value  );        void  putAll  (Map<? extends K,? extends V>  t  );        V  remove  (Object  key  );        int  size  ( );        Collection<V>  values  ( );   } 

Implementations

AbstractMap , HashMap , Hashtable , IdentityHashMap , LinkedHashMap , SortedMap , WeakHashMap , java.util.concurrent.ConcurrentMap , java.util.jar.Attributes

Passed To

Too many methods to list.

Returned By

Too many methods to list.

Type Of

Collections.EMPTY_MAP , java.util.jar.Attributes.map