public interface

Map

java.util.Map<K, V>
Known Indirect Subclasses

Class Overview

A Map is a data structure consisting of a set of keys and values in which each key is mapped to a single value. The class of the objects used as keys is declared when the Map is declared, as is the class of the corresponding values.

A Map provides helper methods to iterate through all of the keys contained in it, as well as various methods to access and update the key/value pairs.

Summary

Nested Classes
public interface Map.Entry<K, V> Map.Entry is a key/value mapping contained in a Map. 
Public Methods
abstract void clear()
Removes all elements from this Map, leaving it empty.
abstract boolean containsKey(Object key)
Returns whether this Map contains the specified key.
abstract boolean containsValue(Object value)
Returns whether this Map contains the specified value.
abstract Set<Entry<K, V>> entrySet()
Returns a Set containing all of the mappings in this Map.
abstract boolean equals(Object object)
Compares the argument to the receiver, and returns true if the specified object is a Map and both Maps contain the same mappings.
abstract V get(Object key)
Returns the value of the mapping with the specified key.
abstract int hashCode()
Returns an integer hash code for the receiver.
abstract boolean isEmpty()
Returns whether this map is empty.
abstract Set<K> keySet()
Returns a set of the keys contained in this Map.
abstract V put(K key, V value)
Maps the specified key to the specified value.
abstract void putAll(Map<? extends K, ? extends V> map)
Copies every mapping in the specified Map to this Map.
abstract V remove(Object key)
Removes a mapping with the specified key from this Map.
abstract int size()
Returns the number of mappings in this Map.
abstract Collection<V> values()
Returns a Collection of the values contained in this Map.

Public Methods

public abstract void clear ()

Removes all elements from this Map, leaving it empty.

Throws
UnsupportedOperationException if removing elements from this Map is not supported.
See Also

public abstract boolean containsKey (Object key)

Returns whether this Map contains the specified key.

Parameters
key the key to search for.
Returns
  • true if this map contains the specified key, false otherwise.

public abstract boolean containsValue (Object value)

Returns whether this Map contains the specified value.

Parameters
value the value to search for.
Returns
  • true if this map contains the specified value, false otherwise.

public abstract Set<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.

Returns
  • a set of the mappings

public abstract boolean equals (Object object)

Compares the argument to the receiver, and returns true if the specified object is a Map and both Maps contain the same mappings.

Parameters
object the Object to compare with this Object.
Returns
  • boolean true if the Object is the same as this Object false if it is different from this Object.
See Also

public abstract V get (Object key)

Returns the value of the mapping with the specified key.

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.

public abstract int hashCode ()

Returns an integer hash code for the receiver. Objects which are equal return the same value for this method.

Returns
  • the receiver's hash.
See Also

public abstract boolean isEmpty ()

Returns whether this map is empty.

Returns
  • true if this map has no elements, false otherwise.
See Also

public abstract 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 Set does not support adding.

Returns
  • a set of the keys.

public abstract V put (K key, V value)

Maps the specified key to the specified value.

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.

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

Copies every mapping in the specified Map to this Map.

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 a value of the specified Map 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.

public abstract V remove (Object key)

Removes a mapping with the specified key from this Map.

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.

public abstract int size ()

Returns the number of mappings in this Map.

Returns
  • the number of mappings in this Map.

public abstract 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(Object), removeAll(Collection), retainAll(Collection), and clear() operations, and it does not support add(E) or addAll(Collection) 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 this Map's entrySet(). The size() method wraps this Map's size() method and the contains(Object) method wraps this Map's containsValue(Object) method.

The collection is created when this method is called at first time and returned in response to all subsequent calls. This method may return different Collection when multiple calls to this method, since it has no synchronization performed.

Returns
  • a collection of the values contained in this map.