Java compact1, compact2, compact3 java.util Interface Map.Entry<K,V>（JDK8）

Method Detail

• 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's remove 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

  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 - new value to be stored in this entry

  Returns:

  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.

• equals

  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.

  Overrides:

  equals in class Object

  Parameters:

  o - object to be compared for equality with this map entry

  Returns:

  true if the specified object is equal to this map entry

  See Also:

  Object.hashCode(), HashMap

• hashCode

  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.

  Overrides:

  hashCode in class Object

  Returns:

  the hash code value for this map entry

  See Also:

  Object.hashCode(), Object.equals(Object), equals(Object)

• comparingByKey

  static <K extends Comparable<? super K>,V> Comparator<Map.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.

  Type Parameters:

  K - the Comparable type of then map keys

  V - the type of the map values

  Returns:

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

  Since:

  1.8

  See Also:

  Comparable

• comparingByValue

  static <K,V extends Comparable<? super V>> Comparator<Map.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.

  Type Parameters:

  K - the type of the map keys

  V - the Comparable type of the map values

  Returns:

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

  Since:

  1.8

  See Also:

  Comparable

• comparingByKey

  static <K,V> Comparator<Map.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.

  Type Parameters:

  K - the type of the map keys

  V - the type of the map values

  Parameters:

  cmp - the key Comparator

  Returns:

  a comparator that compares Map.Entry by the key.

  Since:

  1.8

• comparingByValue

  static <K,V> Comparator<Map.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.

  Type Parameters:

  K - the type of the map keys

  V - the type of the map values

  Parameters:

  cmp - the value Comparator

  Returns:

  a comparator that compares Map.Entry by the value.

  Since:

  1.8