The MAP interface does not inherit the Collection, as follows: Public Interface Map
Interface species definition 14 methods: 1.int size () 2.Boolean iSempty () 3.Boolean ContainSKey (Object value); 5.Object Get (Object Key) 6.object Put (Object) Key, Object Value 7.Object Remove (Object Key) 8.void Putall () 10.Set KeySet () 11.Collection Values () 12.Set entryset () 13.Boolean Equals Object o) 14.Int hashcode ()
Description: GET (Object Key) Method: If there is no specified mapping, return null, but it is also possible that the value is NULL. PUT (Object Key, Object Value) Method: If Key does not exist, add a mapping to NULL. If Key already exists, replace the value value and return the original value (also possible null). REMOVE (Object Key) method: Returns NULL if key does not exist. If Key exists, delete the mapping, returns the deleted Value (also possible NULL). In addition, the interface defines an interface entry: Interface entry {Object getKey (); Object setValue (); boolean equals (Object O); int hashcode ();} This interface represents a key-value Mapping, we can regard a map as a set of Entry.
