Map interface Methods for Java

Common Operating Instructions

　　void Clear ()

Removes all mapping relationships from this mapping (optional).

　　Boolean ContainsKey (Object key)

Returns TRUE if this map contains a mapping relationship for the specified key.

　　Boolean Containsvalue (Object value)

Returns true if the map maps one or more keys to the specified value.

　　Set<map.entry<k,v>> EntrySet ()

Returns a Set view of the mapping relationships contained in this map.

　　Boolean equals (Object O)

Compares whether the specified object is equal to this mapping.

　　V get (Object key)

Returns the value mapped by the specified key, or null if the mapping does not contain a mapping relationship for the key.

　　int Hashcode ()

Returns the hash code value for this mapping.

　　Boolean IsEmpty ()

Returns true if the mapping does not contain a key-value mapping relationship.

　　Set<k> KeySet ()

Returns a Set view of the keys contained in this map.

　　V Put (K key, V value)

Associates the specified value with the specified key in this map (optional operation).

　　void Putall (map<? extends K,? extends v> m)

Copies all mappings from the specified map to this map (optional operation).

　　V Remove (Object key)

If there is a mapping of a key, it is removed from this mapping (optional operation).

　　int size ()

Returns the number of key-value mapping relationships in this map.

　　Collection<v> VALUES ()

Returns a Collection view of the values contained in this map.

General usage of Map

1. Declare a map :

Map map = new HashMap ();

2 . Place values in map , Note: Map is stored in key-value form, such as:

Map.put ("sa", "DD");

3 . To take a value from the map :

String str = map.get ("sa"). ToString,

The result is: str = "DD"

4 . traverse a map to get the key and value from :

Map m= new HashMap ();

For (Object Obj:map.keySet ()) {

Object value = map.get (obj);

}

5 traverse the keyset in a map:

Map map = new HashMap ();
Map.put ("Key", "value");
Set set = Map.keyset ();
Iterator it = Set.iterator ();
Object object = It.next ();
Key
Object.ToString (); Value
Map.get (object);

Map interface Methods for Java