Summary: Ctors | Methods | Inherited Methods | [Expand All]

public class

HashMap

extends AbstractMap<K, V>
implements Serializable Cloneable Map<K, V>

java.lang.Object
↳	java.util.AbstractMap<K, V>
	↳	java.util.HashMap<K, V>

Known Direct Subclasses

LinkedHashMap<K, V>

Class Overview

HashMap is an implementation of Map. All optional operations are supported, adding and removing. Keys and values can be any objects.

Summary

Public Constructors
	HashMap() Constructs a new empty instance of HashMap.
	HashMap(int capacity) Constructs a new instance of HashMap with the specified capacity.
	HashMap(int capacity, float loadFactor) Constructs a new instance of HashMap with the specified capacity and load factor.
	HashMap(Map<? extends K, ? extends V> map) Constructs a new instance of HashMap containing the mappings from the specified Map.

Public Methods
void	clear() Removes all mappings from this HashMap, leaving it empty.
Object	clone() Returns a new HashMap with the same mappings and size as this HashMap.
boolean	containsKey(Object key) Searches this HashMap for the specified key.
boolean	containsValue(Object value) Searches this HashMap for the specified value.
Set<Entry<K, V>>	entrySet() Returns a Set of the mappings contained in this HashMap.
V	get(Object key) Returns the value of the mapping with the specified key.
boolean	isEmpty() Returns if this HashMap has no elements, a size of zero.
Set<K>	keySet() Returns a Set of the keys contained in this HashMap.
V	put(K key, V value) Maps the specified key to the specified value.
void	putAll(Map<? extends K, ? extends V> map) Copies all the mappings in the given map to this map.
V	remove(Object key) Removes a mapping with the specified key from this HashMap.
int	size() Returns the number of mappings in this HashMap.
Collection<V>	values() Returns a Collection of the values contained in this HashMap.

[Expand]

Inherited Methods

From class java.util.AbstractMap

void	clear() Removes all elements from this Map, leaving it empty.
Object	clone() Returns a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	containsKey(Object key) Searches this Map for the specified key.
boolean	containsValue(Object value) Searches this Map for the specified value.
abstract Set<Entry<K, V>>	entrySet() Returns a set view of the mappings contained in this map.
boolean	equals(Object object) Compares the specified object to this Map and answer if they are equal.
V	get(Object key) Returns the value of the mapping with the specified key.
int	hashCode() Returns an integer hash code for the receiver.
boolean	isEmpty() Returns if this Map has no elements, a size of zero.
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.

From class java.lang.Object

Object	clone() Returns a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
void	finalize() Called by the virtual machine when there are no longer any (non-weak) references to the receiver.
final Class<? extends Object>	getClass() Returns the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode() Returns an integer hash code for the receiver.
final void	notify() Causes one thread which is `wait` ing on the receiver to be made ready to run.
final void	notifyAll() Causes all threads which are `wait` ing on the receiver to be made ready to run.
String	toString() Returns a string containing a concise, human-readable description of the receiver.
final void	wait(long time, int frac) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait(long time) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait() Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by `notify` or `notifyAll`).

From interface java.util.Map

abstract void	clear() Removes all elements from this Map, leaving it empty.
abstract boolean	containsKey(Object key) Searches this Map for the specified key.
abstract boolean	containsValue(Object value) Searches this Map for the specified value.
abstract Set<Entry<K, V>>	entrySet() Returns a `Set` whose elements comprise all of the mappings that are to be found in this `Map`.
abstract boolean	equals(Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
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 if this Map has no elements, a size of zero.
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 elements in this Map.
abstract Collection<V>	values() Returns all of the current `Map` values in a `Collection`.

Public Constructors

public HashMap ()

Constructs a new empty instance of HashMap.

public HashMap (int capacity)

Constructs a new instance of HashMap with the specified capacity.

Parameters

capacity	the initial capacity of this HashMap

Throws

IllegalArgumentException	when the capacity is less than zero

public HashMap (int capacity, float loadFactor)

Constructs a new instance of HashMap with the specified capacity and load factor.

Parameters

capacity	the initial capacity
loadFactor	the initial load factor

Throws

IllegalArgumentException	when the capacity is less than zero or the load factor is less or equal to zero

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

Constructs a new instance of HashMap containing the mappings from the specified Map.

Parameters

map	the mappings to add

Public Methods

public void clear ()

Removes all mappings from this HashMap, leaving it empty.

public Object clone ()

Returns a new HashMap with the same mappings and size as this HashMap.

Returns

a shallow copy of this HashMap

public boolean containsKey (Object key)

Searches this HashMap for the specified key.

Parameters

key	the object to search for

Returns

true if key is a key of this HashMap, false otherwise

public boolean containsValue (Object value)

Searches this HashMap for the specified value.

Parameters

value	the object to search for

Returns

true if value is a value of this HashMap, false otherwise

public Set<Entry<K, V>> entrySet ()

Returns a Set of the mappings contained in this HashMap. Each element in the set is a Map.Entry. The set is backed by this HashMap so changes to one are reflected by the other. The set does not support adding.

Returns

a Set of the mappings

public V get (Object key)

Returns the value of the mapping with the specified key. If no entry is found null is returned.

Parameters

key	the key

Returns

the value of the mapping with the specified key, or null if the entry doesn't exist.

public boolean isEmpty ()

Returns if this HashMap has no elements, a size of zero.

Returns

true if this HashMap has no elements, false otherwise

public Set<K> keySet ()

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

Returns

a Set of the keys

public 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

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

Copies all the mappings in the given map to this map. These mappings will replace all mappings that this map had for any of the keys currently in the given map.

Parameters

map	the Map to copy mappings from

Throws

NullPointerException	if the given map is null

public V remove (Object key)

Removes a mapping with the specified key from this HashMap.

Parameters

key	the key of the mapping to remove

Returns

the value of the removed mapping or null if key is not a key in this HashMap

public int size ()

Returns the number of mappings in this HashMap.

Returns

the number of mappings in this HashMap

public Collection<V> values ()

Returns a Collection of the values contained in this HashMap. The collection is backed by this HashMap so changes to one are reflected by the other. The collection does not support adding.

Returns

a Collection of the values

Jan	FEB	Mar
	18
2008	2009	2010

Interfaces

Classes

Enums

Exceptions

HashMap

Class Overview

Summary

Public Constructors

public HashMap ()

public HashMap (int capacity)

Parameters

Throws

public HashMap (int capacity, float loadFactor)

Parameters

Throws

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

Parameters

Public Methods

public void clear ()

See Also

public Object clone ()

Returns

See Also

public boolean containsKey (Object key)

Parameters

Returns

public boolean containsValue (Object value)

Parameters

Returns

public Set<Entry<K, V>> entrySet ()

Returns

public V get (Object key)

Parameters

Returns

public boolean isEmpty ()

Returns

See Also

public Set<K> keySet ()

Returns

public V put (K key, V value)

Parameters

Returns

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

Parameters

Throws

public V remove (Object key)

Parameters

Returns

public int size ()

Returns

public Collection<V> values ()

Returns