public class HashMap extends AbstractMap implements Map, Cloneable, Serializable
Constructor and Description |
---|
HashMap()
Constructs a new empty
HashMap instance. |
HashMap(int capacity)
Constructs a new
HashMap instance with the specified capacity. |
HashMap(int capacity,
float loadFactor)
Constructs a new
HashMap instance with the specified capacity and
load factor. |
HashMap(Map map)
Constructs a new
HashMap instance containing the mappings from
the specified map. |
Modifier and Type | Method and Description |
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void |
clear()
Removes all mappings from this hash map, leaving it empty.
|
Object |
clone()
Returns a shallow copy of this map.
|
boolean |
containsKey(Object key)
Returns whether this map contains the specified key.
|
boolean |
containsValue(Object value)
Returns whether this map contains the specified value.
|
Set |
entrySet()
Returns a set containing all of the mappings in this map.
|
Object |
get(Object key)
Returns the value of the mapping with the specified key.
|
boolean |
isEmpty()
Returns whether this map is empty.
|
Set |
keySet()
Returns a set of the keys contained in this map.
|
Object |
put(Object key,
Object value)
Maps the specified key to the specified value.
|
void |
putAll(Map map)
Copies all the mappings in the specified map to this map.
|
Object |
remove(Object key)
Removes the mapping with the specified key from this map.
|
int |
size()
Returns the number of elements in this map.
|
Collection |
values()
Returns a collection of the values contained in this map.
|
equals, hashCode, toString
public HashMap()
HashMap
instance.public HashMap(int capacity)
HashMap
instance with the specified capacity.capacity
- the initial capacity of this hash map.IllegalArgumentException
- when the capacity is less than zero.public HashMap(int capacity, float loadFactor)
HashMap
instance with the specified capacity and
load factor.capacity
- the initial capacity of this hash map.loadFactor
- the initial load factor.IllegalArgumentException
- when the capacity is less than zero or the load factor is
less or equal to zero.public HashMap(Map map)
HashMap
instance containing the mappings from
the specified map.map
- the mappings to add.public void clear()
public Object clone()
clone
in class AbstractMap
public boolean containsKey(Object key)
containsKey
in interface Map
containsKey
in class AbstractMap
key
- the key to search for.true
if this map contains the specified key,
false
otherwise.public boolean containsValue(Object value)
containsValue
in interface Map
containsValue
in class AbstractMap
value
- the value to search for.true
if this map contains the specified value,
false
otherwise.public Set entrySet()
Map.Entry
. As the set is backed by this map,
changes in one will be reflected in the other.entrySet
in interface Map
entrySet
in class AbstractMap
public Object get(Object key)
get
in interface Map
get
in class AbstractMap
key
- the key.null
if no mapping for the specified key is found.public boolean isEmpty()
isEmpty
in interface Map
isEmpty
in class AbstractMap
true
if this map has no elements, false
otherwise.size()
public Set keySet()
keySet
in interface Map
keySet
in class AbstractMap
public Object put(Object key, Object value)
put
in interface Map
put
in class AbstractMap
key
- the key.value
- the value.null
if there was no such mapping.public void putAll(Map map)
putAll
in interface Map
putAll
in class AbstractMap
map
- the map to copy mappings from.NullPointerException
- if map
is null
.public Object remove(Object key)
remove
in interface Map
remove
in class AbstractMap
key
- the key of the mapping to remove.null
if no mapping
for the specified key was found.public int size()
size
in interface Map
size
in class AbstractMap
public Collection values()
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.
values
in interface Map
values
in class AbstractMap