java.util.Map<K, V> |
Known Indirect Subclasses
AbstractMap
<K, V>,
ArrayMap
<K, V>,
Attributes
,
AuthProvider
,
ConcurrentHashMap
<K, V>,
ConcurrentMap
<K, V>,
ConcurrentNavigableMap
<K, V>,
ConcurrentSkipListMap
<K, V>,
EnumMap
<K extends
Enum
<K>, V>,
HashMap
<K, V>,
Hashtable
<K, V>,
IdentityHashMap
<K, V>,
LinkedHashMap
<K, V>,
NavigableMap
<K, V>,
Properties
,
Provider
,
SortedMap
<K, V>,
TreeMap
<K, V>,
WeakHashMap
<K, V>
|
A
Map
is a data structure consisting of a set of keys and values
in which each key is mapped to a single value. The class of the objects
used as keys is declared when the
Map
is declared, as is the
class of the corresponding values.
A
Map
provides helper methods to iterate through all of the
keys contained in it, as well as various methods to access and update
the key/value pairs.
Nested Classes | |||||||||||
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|
Map.Entry <K, V> |
Map.Entry
is a key/value mapping contained in a
Map
.
|
Public Methods | |||||||||||
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|
Removes all elements from this
Map
, leaving it empty.
|
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|
Returns whether this
Map
contains the specified key.
|
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|
Returns whether this
Map
contains the specified value.
|
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|
Returns a
Set
containing all of the mappings in this
Map
.
|
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|
Compares the argument to the receiver, and returns
true
if the
specified object is a
Map
and both
Map
s contain the same mappings.
|
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|
Returns the value of the mapping with the specified key.
|
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|
Returns an integer hash code for the receiver.
|
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|
Returns whether this map is empty.
|
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|
Returns a set of the keys contained in this
Map
.
|
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|
Maps the specified key to the specified value.
|
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|
Copies every mapping in the specified
Map
to this
Map
.
|
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|
Removes a mapping with the specified key from this
Map
.
|
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|
Returns the number of mappings in this
Map
.
|
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|
Returns a
Collection
of the values contained in this
Map
.
|
Removes all elements from this
Map
, leaving it empty.
UnsupportedOperationException |
if removing elements from this
Map
is not supported.
|
---|
Returns whether this
Map
contains the specified key.
key | the key to search for. |
---|
true
if this map contains the specified key,
false
otherwise.
Returns whether this
Map
contains the specified value.
value | the value to search for. |
---|
true
if this map contains the specified value,
false
otherwise.
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.
Compares the argument to the receiver, and returns
true
if the
specified object is a
Map
and both
Map
s contain the same mappings.
object |
the
Object
to compare with this
Object
.
|
---|
true
if the
Object
is the same as this
Object
false
if it is different from this
Object
.
Returns the value of the mapping with the specified key.
key | the key. |
---|
null
if no mapping for the specified key is found.
Returns an integer hash code for the receiver.
Object
s which are equal
return the same value for this method.
Returns whether this map is empty.
true
if this map has no elements,
false
otherwise.
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.
Maps the specified key to the specified value.
key | the key. |
---|---|
value | the value. |
null
if there was no mapping.
UnsupportedOperationException |
if adding to this
Map
is not supported.
|
---|---|
ClassCastException |
if the class of the key or value is inappropriate for
this
Map
.
|
IllegalArgumentException |
if the key or value cannot be added to this
Map
.
|
NullPointerException |
if the key or value is
null
and this
Map
does
not support
null
keys or values.
|
Copies every mapping in the specified
Map
to this
Map
.
map |
the
Map
to copy mappings from.
|
---|
UnsupportedOperationException |
if adding to this
Map
is not supported.
|
---|---|
ClassCastException |
if the class of a key or a value of the specified
Map
is
inappropriate for this
Map
.
|
IllegalArgumentException |
if a key or value cannot be added to this
Map
.
|
NullPointerException |
if a key or value is
null
and this
Map
does not
support
null
keys or values.
|
Removes a mapping with the specified key from this
Map
.
key | the key of the mapping to remove. |
---|
null
if no mapping
for the specified key was found.
UnsupportedOperationException |
if removing from this
Map
is not supported.
|
---|
Returns the number of mappings in this
Map
.
Map
.
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(Object)
,
?>
)">removeAll(Collection
?>
)
,
?>
)">retainAll(Collection
?>
)
, and
clear()
operations,
and it does not support
add(E)
or
extends E?>
)">addAll(Collection
extends E?>
)
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 this
Map
's
entrySet()
. The
size()
method
wraps this
Map
's
size()
method and the
contains(Object)
method wraps this
Map
's
containsValue(Object)
method.
The collection is created when this method is called at first time and returned in response to all subsequent calls. This method may return different Collection when multiple calls to this method, since it has no synchronization performed.