inheritance - Declaring a superclass variable then instantiating it with a subclass in Java -

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• what mean “program interface”? 29 answers

i little confused , looking clarification on differences , different benefits 2 different approaches declaration , instantiation of map.

what difference between

map<string, string> mymap = new hashmap<string, string>; 

and

hashmap<string, string> mymap = new hashmap<string, string>; 

what benefit or reason declaring superclass variable instantiating subclass?

this called "programming interface". (map interface, not class.) allows code needs map operations not care kind of map is.

you switch out hashmap for, say, treemap if feel it's appropriate, , no other code change.

other similar questions:

• what mean "program interface"?
• what mean program interface?

other references:

• code interface, if interface class
• design principles design patterns talks also.