How to call default interface method from another subclass?

Question

Consider the following:

//Fooable.java
public interface Fooable {
    public default void foo() {
        System.out.println("Fooable::foo");
    }
    //Lots of other non-default methods...
}

//MyFooable.java
public class MyFooable implements Fooable {
    @Override
    public void foo() {
        System.out.println("MyFooable::foo");
    }
    //implements other methods in Fooable...
}

//MyAdvancedFooable.java
public class MyAdvancedFooable extends MyFooable {
    @Override
    public void foo() {
        Fooable.super.foo();
        System.out.println("MyAdvancedFooable::foo");
    }
    public static void main(String[] args) {
        new MyAdvancedFooable().foo();
    }
}

As you can see, I want to call foo() in Fooable from MyAdvancedFooable (a subclass of MyFooable). However, when I try to compile, I get the following error:

MyAdvancedFooable.java:4: error: not an enclosing class: Fooable Fooable.super.foo();

if I try MyAdvancedFooable extends MyFooable implements Fooable I get the following:

MyAdvancedFooable.java:4: error: bad type qualifier Fooable in default super call Fooable.super.foo(); method foo() is overridden in MyFooable

How can I resolve this problem without having to create a new anonymous implementation of Fooable?

This is an interesting question, does anyone know what's the pros of using this type of design? — unobatbayar, Jul 25 '23 at 09:31

score 3 · Answer 1 · answered May 01 '17 at 12:21

3

You can only call a method one level up so you would need

Fooable.super.foo();

in MyFooable, while just calling super.foo() in MyAdvancedFooable

answered May 01 '17 at 12:21

Reimeus

158,255
15
216
276

Fan Zhou · Answer 2 · 2023-07-31T06:23:45.710

You can do MyAdvancedFooable extends MyFooable implements Fooable. Then create another interface, AnotherFooable, for example, instead of Fooable, as follows:

public interface AnotherFooable implements Fooable {
    public default void foo() {
        Fooable.super.foo();
    }
}

public class MyAdvancedFooable extends MyFooable implements AnotherFooable {
    @Override
    public void foo() {
        AnotherFooable.super.foo();
        System.out.println("MyAdvancedFooable::foo");
    }
}

See: Create another interface

score 0 · Answer 3 · answered May 01 '17 at 12:20

0

You need to use just super.foo() or this.super.foo() as it is the parent of the object and not of the class as implied by Fooable.super.foo().

answered May 01 '17 at 12:20

Shakhar

432
3
12

1

The OP wants to call the `foo()` method from the interface. Your solution would call the method in `MyFooable` instead – Robin Topper May 01 '17 at 12:23

How to call default interface method from another subclass?

3 Answers3