| java.lang.Object | ||
| ↳ | java.util.AbstractMap<K, V> | |
| ↳ | java.util.HashMap<K, V> | |
 Known Direct Subclasses
LinkedHashMap<K, V>
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Class Overview
HashMap is an implementation of Map. All optional operations (adding and removing) are supported. Keys and values can be any objects.
Summary
| Public Constructors | |||||||||||
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HashMap()
Constructs a new empty
HashMap instance. | |||||||||||
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HashMap(int capacity)
Constructs a new
HashMap instance with the specified capacity. | |||||||||||
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HashMap(int capacity, float loadFactor)
Constructs a new
HashMap instance with the specified capacity and
load factor. | |||||||||||
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HashMap(Map<? extends K, ? extends V> map)
Constructs a new
HashMap instance containing the mappings from the
specified map. | |||||||||||
| Public Methods | |||||||||||
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| void |
clear()
Removes all mappings from this hash map, leaving it empty.
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| boolean |
containsKey(Object key)
Returns whether this map contains the specified key.
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| boolean |
containsValue(Object value)
Returns whether this map contains the specified value.
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| Set<Entry<K, V>> |
entrySet()
Returns a set containing all of the mappings in this map.
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| V |
get(Object key)
Returns the value of the mapping with the specified key.
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| boolean |
isEmpty()
Returns whether this map is empty.
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| Set<K> |
keySet()
Returns a set of the keys contained in this map.
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| V |
put(Object key, Object value)
Maps the specified key to the specified value.
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| void |
putAll(Map<? extends K, ? extends V> map)
Copies all the mappings in the specified map to this map.
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| V |
remove(Object key)
Removes the mapping with the specified key from this map.
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| int |
size()
Returns the number of elements in this map.
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| Collection<V> |
values()
Returns a collection of the values contained in this map.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.util.AbstractMap
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From class
java.lang.Object
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From interface
java.util.Map
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Public Constructors
public HashMap ()
Constructs a new empty HashMap instance.
public HashMap (int capacity)
Constructs a new HashMap instance with the specified capacity.
Parameters
| capacity | the initial capacity of this hash map. |
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Throws
| IllegalArgumentException | when the capacity is less than zero. |
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public HashMap (int capacity, float loadFactor)
Constructs a new HashMap instance with the specified capacity and
load factor.
Parameters
| capacity | the initial capacity of this hash map. |
|---|---|
| loadFactor | the initial load factor. |
Throws
| IllegalArgumentException | when the capacity is less than zero or the load factor is less or equal to zero. |
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public HashMap (Map<? extends K, ? extends V> map)
Constructs a new HashMap instance containing the mappings from the
specified map.
Parameters
| map | the mappings to add. |
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Public Methods
public void clear ()
public boolean containsKey (Object key)
Returns whether this map contains the specified key.
Parameters
| key | the key to search for. |
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Returns
trueif this map contains the specified key,falseotherwise.
public boolean containsValue (Object value)
Returns whether this map contains the specified value.
Parameters
| value | the value to search for. |
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Returns
trueif this map contains the specified value,falseotherwise.
public 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 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
nullif no mapping for the specified key is found.
public boolean isEmpty ()
Returns whether this map is empty.
Returns
trueif this map has no elements,falseotherwise.
See Also
public 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 V put (Object key, Object 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
nullif there was no such mapping.
public void putAll (Map<? extends K, ? extends V> map)
Copies all the mappings in the specified 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. |
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Throws
| NullPointerException | if map is null.
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public V remove (Object key)
Removes the mapping with the specified key from this map.
Parameters
| key | the key of the mapping to remove. |
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Returns
- the value of the removed mapping or
nullif no mapping for the specified key was found.
public int size ()
Returns the number of elements in this map.
Returns
- the number of elements in this map.
public 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, removeAll, retainAll and clear operations, and it does not support add or addAll 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 map's entrySet(). The size method wraps the map's size
method and the contains method wraps the map's containsValue method.
The collection is created when this method is called for the first time and returned in response to all subsequent calls. This method may return different collections when multiple concurrent calls occur, since no synchronization is performed.
Returns
- a collection of the values contained in this map.