1-An object that maps keys to values.
2-A map cannot contain duplicate keys;
3-each key can map to at most one value.
4-both the key and the value are objects.
5-The Map interface is provide three collection view
1-collections of value
2-set of keys
3-set of key -value mappings
6-Four main classes which are implemented the Map interface
1-HashMap
2-Hashtable
3-LinkedHashMap
4-TreeMap
7-All general-purpose map implementation classes should provide two "standard" constructors:
1-a void (no arguments) constructor which creates an empty map
2-a constructor with a single argument of type Map,
3-which creates a new map with the same key-value mappings as its argument.
8-method in this interface
1- boolean containsKey(Object key);
2-boolean containsValue(Object value);
3-V get(Object key);
4-V put(K key, V value);
5-V setValue(V value);
6-V getValue();
7-boolean equals(Object o);
8-int hashCode();
