A class implementing common method of interface

Question

There is just one question in which i am got confused... There are two interfaces A , B which contains the same method methodC()...and C class implements A&B. which interface method it should be implemented A or B
Now as per my analysis i have lyk say below class..

 interface  A {
        /**
         * Doc A
         * **/
        public void MethodA();

        public String MethodB();

    }

    interface  B {
        /**
         * Doc B
         * **/
        public String MethodA();

        public void MethodB();
    }

    class lucy implements A,B{

        @Override
        public String MethodA() {
            //To change body of implemented methods use File | Settings | File Templates.
            return null;
        }

        @Override
        public String MethodB() {
            //To change body of implemented methods use File | Settings | File Templates.
            return null;
        }
    }

Output:

Hello Hello

@LuiggiMendoza well forgot the code since it is raw coded , major concern is concept — user3875672
Again: this won't compile, that's why this question at all is strange. Test it. — Luiggi Mendoza
does it matter? methods from A or B does not have implementations. — Adi
Yes it matters. Because if you test it, the compiler will give you the answer: you can't. — Luiggi Mendoza

Unknown Unknown · Accepted Answer · 2014-09-01T06:36:07

Let's assume we have an interface:

public interface A {

    public void firstMethod();

    public void secondMethod();
}

and this interface:

public interface B {

    public void firstMethod();

    public void secondMethod();
}

If you make a class, that implements both of these interfaces, it will be compiled and work ok.

public class MyClass implements A, B {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
    }

    @Override
    public void firstMethod() {
        // some code here
    }

    @Override
    public void secondMethod() {
        // some code here
    }
}

But if you add methods firstMethod() and secondMethod() to the MyClass but with different return type, it won't compile.

public class MyClass implements A, B {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
    }

    public String firstMethod() {
        return "";
    }

    public String secondMethod() {
        return "";
    }

    @Override
    public void firstMethod() {
        // some code here
    }

    @Override
    public void secondMethod() {
        // some code here
    }
}

To compose method signature Java uses method parameters, but not the return type. And it will lead to "method is already defined" error. Because from Java's point of view methods: void firstMethod(); and String firstMethod(); (the same for the secondMethod() method) have the same signatures.

A class implementing common method of interface

1 Answers