Added in API level 1
Summary: Methods

Map.Entry

public static interface Map.Entry

java.util.Map.Entry<K, V>

A map entry (key-value pair). The Entry may be unmodifiable, or the value may be modifiable if the optional 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.

See also:

Summary

Public methods

static <K, V> Comparator<Entry<K, V>> comparingByKey(Comparator<? super K> cmp)

Returns a comparator that compares Map.Entry by key using the given Comparator.

static <K extends Comparable<? super K>, V> Comparator<Entry<K, V>> comparingByKey()

Returns a comparator that compares Map.Entry in natural order on key.

static <K, V> Comparator<Entry<K, V>> comparingByValue(Comparator<? super V> cmp)

Returns a comparator that compares Map.Entry by value using the given Comparator.

static <K, V extends Comparable<? super V>> Comparator<Entry<K, V>> comparingByValue()

Returns a comparator that compares Map.Entry in natural order on value.

static <K, V> Entry<K, V> copyOf(Entry<? extends K, ? extends V> e)

Returns a copy of the given Map.Entry.

abstract boolean equals(Object o)

Compares the specified object with this entry for equality.

abstract K getKey()

Returns the key corresponding to this entry.

abstract V getValue()

Returns the value corresponding to this entry.

abstract int hashCode()

Returns the hash code value for this map entry.

abstract V setValue(V value)

Replaces the value corresponding to this entry with the specified value (optional operation).

Public methods

comparingByKey

Added in API level 24 
public static Comparator<Entry<K, V>> comparingByKey (Comparator<? super K> cmp)

Returns a comparator that compares Map.Entry by key using the given Comparator.

The returned comparator is serializable if the specified comparator is also serializable.

Parameters
cmp Comparator: the key Comparator
Returns
Comparator<Entry<K, V>> a comparator that compares Map.Entry by the key.

comparingByKey

Added in API level 24 
public static Comparator<Entry<K, V>> comparingByKey ()

Returns a comparator that compares Map.Entry in natural order on key.

The returned comparator is serializable and throws NullPointerException when comparing an entry with a null key.

Returns
Comparator<Entry<K, V>> a comparator that compares Map.Entry in natural order on key.

See also:

comparingByValue

Added in API level 24 
public static Comparator<Entry<K, V>> comparingByValue (Comparator<? super V> cmp)

Returns a comparator that compares Map.Entry by value using the given Comparator.

The returned comparator is serializable if the specified comparator is also serializable.

Parameters
cmp Comparator: the value Comparator
Returns
Comparator<Entry<K, V>> a comparator that compares Map.Entry by the value.

comparingByValue

Added in API level 24 
public static Comparator<Entry<K, V>> comparingByValue ()

Returns a comparator that compares Map.Entry in natural order on value.

The returned comparator is serializable and throws NullPointerException when comparing an entry with null values.

Returns
Comparator<Entry<K, V>> a comparator that compares Map.Entry in natural order on value.

See also:

copyOf

Added in API level 35 
public static Entry<K, V> copyOf (Entry<? extends K, ? extends V> e)

Returns a copy of the given Map.Entry. The returned instance is not associated with any map. The returned instance has the same characteristics as instances returned by the Map::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 a Map.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 or Map::entry, calling copyOf will generally not create another copy.
Parameters
e Entry: the entry to be copied
Returns
Entry<K, V> a map entry equal to the given entry
Throws
NullPointerException if e is null or if either of its key or value is null

equals

Added in API level 1 
public abstract boolean equals (Object o)

Compares the specified object with this entry for equality. Returns true if the given object is also a map entry and the two entries represent the same mapping. More formally, two entries e1 and e2 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 the equals method works properly across different implementations of the Map.Entry interface.

Parameters
o Object: object to be compared for equality with this map entry
Returns
boolean true if the specified object is equal to this map entry

getKey

Added in API level 1 
public abstract K getKey ()

Returns the key corresponding to this entry.

Returns
K 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

Added in API level 1 
public abstract V getValue ()

Returns the value corresponding to this entry. If the mapping has been removed from the backing map (by the iterator's remove operation), the results of this call are undefined.

Returns
V 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.

hashCode

Added in API level 1 
public abstract int hashCode ()

Returns the hash code value for this map entry. The hash code of a map entry e is defined to be: 

     (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
     (e.getValue()==null ? 0 : e.getValue().hashCode())
This ensures that e1.equals(e2) implies that e1.hashCode()==e2.hashCode() for any two Entries e1 and e2, as required by the general contract of Object.hashCode.

Returns
int the hash code value for this map entry

setValue

Added in API level 1 
public abstract V setValue (V value)

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's remove operation).

Parameters
value V: new value to be stored in this entry
Returns
V old value corresponding to the entry
Throws
UnsupportedOperationException if the put operation is not supported by the backing map
ClassCastException if the class of the specified value prevents it from being stored in the backing map
NullPointerException if the backing map does not permit null values, and the specified value is null
IllegalArgumentException if some property of this value prevents it from being stored in the backing map
IllegalStateException implementations may, but are not required to, throw this exception if the entry has been removed from the backing map.