Reference:Java.util.HashMap

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java.util
public class java.util.HashMap

java.lang.Object
java.util.AbstractMap Map
java.util.HashMap Serializable Cloneable Map
HashMap is an implementation of Map. All optional operations are supported, adding and removing. Keys and values can be any objects.

Contents

[edit] Known Direct Subclasses

LinkedHashMap

[edit] Summary

[edit] 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 map)
Constructs a new instance of HashMap containing the mappings from the specified Map.

[edit] Public Methods

        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.
        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   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 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 ()
Answers the number of mappings in this HashMap.
        Collection   values ()
Answers a Collection of the values contained in this HashMap.

[edit] Methods inherited from class java.util.AbstractMap
clear, clone, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, )">putAll, remove, size, toString, values
[edit] Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
[edit] Methods inherited from interface java.util.Map

clear, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, )">putAll, remove, size, values

[edit] Details

[edit] Public Constructors

[edit] public HashMap()

Constructs a new empty instance of HashMap.

[edit] 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

[edit] 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

[edit] public HashMap(Map map)

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

Parameters

map the mappings to add

[edit] Public Methods

[edit] public void clear()

Removes all mappings from this HashMap, leaving it empty.

See Also

[edit] public Object clone()

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

Returns

  • a shallow copy of this HashMap

See Also

[edit] 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

[edit] 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

[edit] 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 reflected by the other. The set does not support adding.

Returns

  • a Set of the mappings

[edit] public V get(Object key)

Answers the value of the mapping with the specified key.

Parameters

key the key

Returns

  • the value of the mapping with the specified key

[edit] public boolean isEmpty()

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

Returns

  • true if this HashMap has no elements, false otherwise

See Also

[edit] 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 reflected by the other. The set does not support adding.

Returns

  • a Set of the keys

[edit] 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

[edit] public void putAll(Map 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

[edit] 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

[edit] public int size()

Answers the number of mappings in this HashMap.

Returns

  • the number of mappings in this HashMap

[edit] 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 reflected by the other. The collection does not support adding.

Returns

  • a Collection of the values

[edit] References

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