Interface Map.Entry<K,V>
- Type Parameters:
K
- the type of the keyV
- the type of the value
- All Known Implementing Classes:
AbstractMap.SimpleEntry
,AbstractMap.SimpleImmutableEntry
setValue
method is
implemented. The Entry may be independent of any map, or it may represent
an entry of the entry-set view of a map.
An Entry maintains a connection to its underlying map if the Entry was obtained by
iterating the Map.entrySet()
view of a map, either explicitly by using an
Iterator
or implicitly via the enhanced for
statement. This connection
to the backing map is valid only during iteration of the entry-set view. During
the iteration, if supported by the backing map, a change to an Entry's value via
the setValue
method will be visible in the backing map.
The behavior of such an Entry is undefined outside of iteration of the map's entry-set
view. It is also undefined if the backing map has been modified after the Entry was
returned by the iterator, except through the setValue
method. In addition,
a change to the value of a mapping in the backing map might or might not be
visible in the corresponding Entry of the entry-set view.
An Entry may also be obtained from a map's entry-set view by other means, for
example, using the
parallelStream
,
stream
,
spliterator
methods,
any of the
toArray
overloads,
or by copying the entry-set view into another collection. It is unspecified whether
the obtained Entry instances are connected to the underlying map, whether changes
to such an Entry will affect the underlying the map and vice-versa, and whether
such an Entry supports the optional setValue
method.
In addition, an Entry may be obtained directly from a map, for example via calls
to methods directly on the NavigableMap
interface. An entry thus obtained
is generally not connected to the map and is an unmodifiable snapshot of the mapping
as of the time of the call. Such an Entry also does not generally support the
setValue
method.
An Entry obtained by direct construction of the AbstractMap.SimpleEntry
or AbstractMap.SimpleImmutableEntry
classes or from a call to the
Map.entry
or Map.Entry.copyOf
methods
is not connected to any map.
- API Note:
- The exact behavior of Entry instances obtained from a map's entry-set view other than
via iteration varies across different map implementations; some are connected to the
backing map, and some are not. To guarantee that an Entry is disconnected from its
backing map, use the
copyOf
method. For example, the following creates a snapshot of a map's entries that is guaranteed not to change even if the original map is modified:var entries = map.entrySet().stream().map(Map.Entry::copyOf).toList()
- Since:
- 1.2
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptionstatic <K extends Comparable<? super K>,
V>
Comparator<Map.Entry<K, V>> Returns a comparator that comparesMap.Entry
in natural order on key.static <K,
V> Comparator <Map.Entry<K, V>> comparingByKey
(Comparator<? super K> cmp) Returns a comparator that comparesMap.Entry
by key using the givenComparator
.static <K,
V extends Comparable<? super V>>
Comparator<Map.Entry<K, V>> Returns a comparator that comparesMap.Entry
in natural order on value.static <K,
V> Comparator <Map.Entry<K, V>> comparingByValue
(Comparator<? super V> cmp) Returns a comparator that comparesMap.Entry
by value using the givenComparator
.static <K,
V> Map.Entry <K, V> Returns a copy of the givenMap.Entry
.boolean
Compares the specified object with this entry for equality.getKey()
Returns the key corresponding to this entry.getValue()
Returns the value corresponding to this entry.int
hashCode()
Returns the hash code value for this map entry.Replaces the value corresponding to this entry with the specified value (optional operation).
-
Method Details
-
getKey
K getKey()Returns the key corresponding to this entry.- Returns:
- the key corresponding to this entry
- Throws:
IllegalStateException
- implementations may, but are not required to, throw this exception if the entry has been removed from the backing map.
-
getValue
V getValue()Returns the value corresponding to this entry. If the mapping has been removed from the backing map (by the iterator'sremove
operation), the results of this call are undefined.- Returns:
- the value corresponding to this entry
- Throws:
IllegalStateException
- implementations may, but are not required to, throw this exception if the entry has been removed from the backing map.
-
setValue
Replaces the value corresponding to this entry with the specified value (optional operation). (Writes through to the map.) The behavior of this call is undefined if the mapping has already been removed from the map (by the iterator'sremove
operation).- Parameters:
value
- new value to be stored in this entry- Returns:
- old value corresponding to the entry
- Throws:
UnsupportedOperationException
- if theput
operation is not supported by the backing mapClassCastException
- if the class of the specified value prevents it from being stored in the backing mapNullPointerException
- if the backing map does not permit null values, and the specified value is nullIllegalArgumentException
- if some property of this value prevents it from being stored in the backing mapIllegalStateException
- implementations may, but are not required to, throw this exception if the entry has been removed from the backing map.
-
equals
Compares the specified object with this entry for equality. Returnstrue
if the given object is also a map entry and the two entries represent the same mapping. More formally, two entriese1
ande2
represent the same mapping if(e1.getKey()==null ? e2.getKey()==null : e1.getKey().equals(e2.getKey())) && (e1.getValue()==null ? e2.getValue()==null : e1.getValue().equals(e2.getValue()))
This ensures that theequals
method works properly across different implementations of theMap.Entry
interface. -
hashCode
int hashCode()Returns the hash code value for this map entry. The hash code of a map entrye
is defined to be:(e.getKey()==null ? 0 : e.getKey().hashCode()) ^ (e.getValue()==null ? 0 : e.getValue().hashCode())
This ensures thate1.equals(e2)
implies thate1.hashCode()==e2.hashCode()
for any two Entriese1
ande2
, as required by the general contract ofObject.hashCode
. -
comparingByKey
Returns a comparator that comparesMap.Entry
in natural order on key.The returned comparator is serializable and throws
NullPointerException
when comparing an entry with a null key.- Type Parameters:
K
- theComparable
type of then map keysV
- the type of the map values- Returns:
- a comparator that compares
Map.Entry
in natural order on key. - Since:
- 1.8
- See Also:
-
comparingByValue
Returns a comparator that comparesMap.Entry
in natural order on value.The returned comparator is serializable and throws
NullPointerException
when comparing an entry with null values.- Type Parameters:
K
- the type of the map keysV
- theComparable
type of the map values- Returns:
- a comparator that compares
Map.Entry
in natural order on value. - Since:
- 1.8
- See Also:
-
comparingByKey
Returns a comparator that comparesMap.Entry
by key using the givenComparator
.The returned comparator is serializable if the specified comparator is also serializable.
- Type Parameters:
K
- the type of the map keysV
- the type of the map values- Parameters:
cmp
- the keyComparator
- Returns:
- a comparator that compares
Map.Entry
by the key. - Since:
- 1.8
-
comparingByValue
Returns a comparator that comparesMap.Entry
by value using the givenComparator
.The returned comparator is serializable if the specified comparator is also serializable.
- Type Parameters:
K
- the type of the map keysV
- the type of the map values- Parameters:
cmp
- the valueComparator
- Returns:
- a comparator that compares
Map.Entry
by the value. - Since:
- 1.8
-
copyOf
Returns a copy of the givenMap.Entry
. The returned instance is not associated with any map. The returned instance has the same characteristics as instances returned by theMap::entry
method.- API Note:
- An instance obtained from a map's entry-set view has a connection to that map.
The
copyOf
method may be used to create aMap.Entry
instance, containing the same key and value, that is independent of any map. - Implementation Note:
- If the given entry was obtained from a call to
copyOf
orMap::entry
, callingcopyOf
will generally not create another copy. - Type Parameters:
K
- the type of the keyV
- the type of the value- Parameters:
e
- the entry to be copied- Returns:
- a map entry equal to the given entry
- Throws:
NullPointerException
- if e is null or if either of its key or value is null- Since:
- 17
-