Map.Entry (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档

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Java™ Platform
Standard Ed. 6

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java.util
Interface Map.Entry<K,V>

All Known Implementing Classes:: AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry

Enclosing interface:: Map<K,V>

public static interface Map.Entry<K,V>

A map entry (key-value pair). The Map.entrySet method returns a collection-view of the map, whose elements are of this class. The only way to obtain a reference to a map entry is from the iterator of this collection-view. These Map.Entry objects are valid only for the duration of the iteration; more formally, the behavior of a map entry is undefined if the backing map has been modified after the entry was returned by the iterator, except through the setValue operation on the map entry.

Since:: 1.2
See Also:: Map.entrySet()

Method Summary

boolean equals(Object o)
          Compares the specified object with this entry for equality.

K getKey()
          Returns the key corresponding to this entry.

V getValue()
          Returns the value corresponding to this entry.

int hashCode()
          Returns the hash code value for this map entry.

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

Method Summary
`boolean`	`equals(Object o)` Compares the specified object with this entry for equality.
`K`	`getKey()` Returns the key corresponding to this entry.
`V`	`getValue()` Returns the value corresponding to this entry.
`int`	`hashCode()` Returns the hash code value for this map entry.
`V`	`setValue(V value)` Replaces the value corresponding to this entry with the specified value (optional operation).

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(), Hashtable

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)