java.util
Class HashMap<K,V>

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

Type Parameters:

K - the type of the keys this map will contain

V - the type of the values this map will contain

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>

Direct Known Subclasses:

LinkedHashMap

public class HashMap<K,V>
extends AbstractMap<K,V>
implements Map<K,V>, Cloneable, Serializable

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

See Also:

Serialized Form

Constructor Summary

HashMap()
Contructs 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.

Method Summary

void	clear() Removes all mappings from this HashMap, leaving it empty.
Object	clone() Answers 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<Map.Entry<K,V>>	entrySet() Answers a Set of the mappings contained in this HashMap.
V	get(Object key) Answers the value of the mapping with the specified key.
boolean	isEmpty() Answers if this HashMap has no elements, a size of zero.
Set<K>	keySet() Answers 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 every mapping in the specified Map to this HashMap.
V	remove(Object key) Removes a mapping with the specified key from this HashMap.
int	size() Answers the number of mappings in this HashMap.
Collection<V>	values() Answers a Collection of the values contained in this HashMap.

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Constructor Detail

HashMap

public HashMap()

Contructs a new empty instance of HashMap.

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

HashMap

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

HashMap

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

Method Detail

clear

public void clear()

Removes all mappings from this HashMap, leaving it empty.

Specified by:

clear in interface Map<K,V>

Overrides:

clear in class AbstractMap<K,V>

See Also:

isEmpty(), size()

clone

public Object clone()

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

Overrides:

clone in class AbstractMap<K,V>

Returns:

a shallow copy of this HashMap

See Also:

Cloneable

containsKey

public boolean containsKey(Object key)

Searches this HashMap for the specified key.

Specified by:

containsKey in interface Map<K,V>

Overrides:

containsKey in class AbstractMap<K,V>

Parameters:

key - the object to search for

Returns:

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

containsValue

public boolean containsValue(Object value)

Searches this HashMap for the specified value.

Specified by:

containsValue in interface Map<K,V>

Overrides:

containsValue in class AbstractMap<K,V>

Parameters:

value - the object to search for

Returns:

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

entrySet

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

Answers 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 relected by the other. The set does not support adding.

Specified by:

entrySet in interface Map<K,V>

Specified by:

entrySet in class AbstractMap<K,V>

Returns:

a Set of the mappings

get

public V get(Object key)

Answers the value of the mapping with the specified key.

Specified by:

get in interface Map<K,V>

Overrides:

get in class AbstractMap<K,V>

Parameters:

key - the key

Returns:

the value of the mapping with the specified key

isEmpty

public boolean isEmpty()

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

Specified by:

isEmpty in interface Map<K,V>

Overrides:

isEmpty in class AbstractMap<K,V>

Returns:

true if this HashMap has no elements, false otherwise

See Also:

size()

keySet

@SuppressWarnings(value="all")
public Set<K> keySet()

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

Specified by:

keySet in interface Map<K,V>

Overrides:

keySet in class AbstractMap<K,V>

Returns:

a Set of the keys

put

public V put(K key,
             V value)

Maps the specified key to the specified value.

Specified by:

put in interface Map<K,V>

Overrides:

put in class AbstractMap<K,V>

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

putAll

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

Copies every mapping in the specified Map to this HashMap.

Specified by:

putAll in interface Map<K,V>

Overrides:

putAll in class AbstractMap<K,V>

Parameters:

map - the Map to copy mappings from

remove

public V remove(Object key)

Removes a mapping with the specified key from this HashMap.

Specified by:

remove in interface Map<K,V>

Overrides:

remove in class AbstractMap<K,V>

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

size

public int size()

Answers the number of mappings in this HashMap.

Specified by:

size in interface Map<K,V>

Overrides:

size in class AbstractMap<K,V>

Returns:

the number of mappings in this HashMap

values

@SuppressWarnings(value="all")
public Collection<V> values()

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

Specified by:

values in interface Map<K,V>

Overrides:

values in class AbstractMap<K,V>

Returns:

a Collection of the values