java collections: Map

Inheritance

Map

• Map isMapping interface, The content is stored in the MapKey-value pairs(key-value)，Map map can not contain duplicate keys; each key can only be mapped to a value at most。
• Map's implementation classes should provide two "standard" constructors:First, void (no argument) constructor, creates an empty map；Second, the method is configured with a single argument of type Map, therewith for creating a parameter with the same key - new map value mappings.
• Map provides interfaces are used to return a set of keys or a set of key values ​​- set value mappings.
• the entrySet () Returns theKey - Value SetofSet collection
• keySet () Returns theKeysetofSet collection
• values ​​() returns the userValue SetofCollection collection
• Because the Map can not contain duplicate keys; each key can only be mapped to a value at most. and so,Key - value set, the key set is Set, the value of the collection Collection。

Entry

• Map.Entry is an interface inside of the Map, Map.Entry isKey-value pairs, Map by the entrySet () Gets the value pairs Map.Entry set, thereby achieving the operation of the key value through the set.

AbstractMap

• AbstractMap isMap inherited from an abstract class that implements most of the Map API
• To achieve unmodifiable map, simply extend this class and provide implementations can entrySet method, which returns a mapping relationship set view map. Typically, the returned set will in turn be implemented on AbstractSet. This set does not support the add () or remove () method, the iterator does not support the remove () method.
• To implement a modifiable map, you must put another override the methods of this class (or they will throw UnsupportedOperationException), entrySet (). Iterator () returns the iterator must additionally implement its remove method.

SortedMap

• SortedMap is inherited Map interface. Content is SortedMapSort of key-value pairsSorting method is by a comparator (Comparator)
• There are two types of SortedMap Sort by:Natural order OrUser specified comparator. Ordered insertion SortedMap all elements must implement Comparable interface (or designated comparator accepted).

NavigableMap

• NavigableMap inherited from SortedMap interface. Compared to SortedMap, NavigableMap a series of navigation method; such as "greater than obtaining / object of certain other key", "key Get less than / equal to a certain object on the" like.

Dictionary

• NavigableMap key JDK 1.0 is defined for the interface, including the basic functions of the operation keys.