Question

I’ve a code:

interface My {
    //this is left empty
}

class Test implements My {
    public static void main(String[] args){
        My m=new Test();
        String str=m.toString();    //how reference variable m calls toString() in Test even it is not in My?
        System.out.println(str);
        str=m.show();    //Error:
        System.out.println(str);
    }

    public String toString(){
        return "Hello";
    }

    public String show(){
        return "World";
    }
}

The error at str=m.show() is cannot find symbol str=m.show() and location: variable m of type My.

My question is how the m.toString() does not report any error but m.show() report such error.

Answer 1

toString() is defined in Object. Any concrete implementation of an interface will also extend Object, so you can call any method declared in Object.