CODEWITHSUNDEEP
javainheritanceoverridingoverloading
user3885166
user3885166

Reputation: 215

Overriding methods and weird behavior

I have 2 classes, one which extends the second one and overrides some of the methods of the parent. When I call fs.m(ff) I got a weird result, and I can't figure out why does it happen. type First fs shouldn't have access to class Second methods, even if we assigned a new Second object to them, unless we casted it like that - (Second) fs.m(ff). Could anyone please explain why does this code produce output "override"?

public class Main {

    public static void main(String[] args) {
        First ff = new First();
        First fs = new Second();
        Second ss = new Second();

        System.out.println( fs.m(ff));
    }
}


public class First {
    public String m(First x){
        return "default";
    }

    public String m(First x, First y){
        return "default";
    }
}

public class Second extends First{
    public String m(Second x){
        return "overload";
    }

    public String m(First x){
        return "override";
    }

    public String m(First x, Second y){
        return "???";
    }
}

Upvotes: 2

Views: 50

Answers (2)

Paul John
Paul John

Reputation: 1661

Fs is actually pointing a Second Object (fs is a reference to an object of type Second). So when you call fs.m(ff) it is actually calling the object on Second due to dynamic binding (override).

Upvotes: 0

Eran
Eran

Reputation: 393771

The method invoked for fs.m(ff) is determined by the runtime type of fs. That runtime type is Second, and since Second overrides the public String m(First x) method, that method is executed.

fs has access do the methods declared in First class, since it is of type First, but during runtime, the actual methods that get executed depend on whether those methods are overridden by the run-time type of the instance assigned to fs, which is Second.

Upvotes: 3

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