java.util
Class HashMap

java.lang.Object
  |
  +--java.util.AbstractMap
        |
        +--java.util.HashMap

All Implemented Interfaces:

Cloneable, Map, Serializable

Direct Known Subclasses:

LinkedHashMap

public class HashMap

extends AbstractMap

implements Map, 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

Nested Class Summary

Nested classes inherited from class java.util.Map

Map.Entry

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 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	entrySet() Answers a Set of the mappings contained in this HashMap.
Object	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	keySet() Answers a Set of the keys contained in this HashMap.
Object	put(Object key, Object value) Maps the specified key to the specified value.
void	putAll(Map map) Copies every mapping in the specified Map to this HashMap.
Object	remove(Object key) Removes a mapping with the specified key from this HashMap.
int	size() Answers the number of mappings in this HashMap.
Collection	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 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

Overrides:

clear in class AbstractMap

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

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

Overrides:

containsKey in class AbstractMap

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

Overrides:

containsValue in class AbstractMap

Parameters:

value - the object to search for

Returns:

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

entrySet

public Set 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

Specified by:

entrySet in class AbstractMap

Returns:

a Set of the mappings

get

public Object get(Object key)

Answers the value of the mapping with the specified key.

Specified by:

get in interface Map

Overrides:

get in class AbstractMap

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

Overrides:

isEmpty in class AbstractMap

Returns:

true if this HashMap has no elements, false otherwise

See Also:

size()

keySet

public Set 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

Overrides:

keySet in class AbstractMap

Returns:

a Set of the keys

put

public Object put(Object key,
                  Object value)

Maps the specified key to the specified value.

Specified by:

put in interface Map

Overrides:

put in class AbstractMap

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 map)

Copies every mapping in the specified Map to this HashMap.

Specified by:

putAll in interface Map

Overrides:

putAll in class AbstractMap

Parameters:

map - the Map to copy mappings from

remove

public Object remove(Object key)

Removes a mapping with the specified key from this HashMap.

Specified by:

remove in interface Map

Overrides:

remove in class AbstractMap

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

Overrides:

size in class AbstractMap

Returns:

the number of mappings in this HashMap

values

public Collection 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

Overrides:

values in class AbstractMap

Returns:

a Collection of the values