What happens, if two interfaces contain the same default method?

Question

If I have two interface with the same default method and both are implementing with a class/ See this program.

interface alpha {
  default void reset() {
    System.out.println("This is alpha version of default");
  }
}

interface beta {
  default void reset() {
    System.out.println("This is beta version of default");
  }
}

class MyClass implements alpha, beta {
  void display() {
    System.out.println("This is not default");
  }
}

class main_class {
  public static void main(String args[]) {
    MyClass ob = new MyClass();
    ob.reset();
    ob.display();
  }  
}

then what will happen? And also I am getting unrelated error with this program.

Interface are pure abstract and just only declarations not implementations. — Shriram, Dec 25 '14 at 16:42
@Shriram In Java 8 they can contain implementations using default methods — Bohuslav Burghardt, Dec 25 '14 at 16:42
I suspect that "unrelated error" is telling you the answer to this question. — chrylis -cautiouslyoptimistic-, Dec 25 '14 at 16:53

sol4me · Accepted Answer · 2014-12-26T13:11:43.887

7

You cannot implement multiple interfaces having same signature of Java 8 default methods (without overriding explicitly in child class)

. You can solve it by implementing the method E.g.

class MyClass implements alpha, beta {
  void display() {
    System.out.println("This is not default");
  }

  @Override
  public void reset() {
    //in order to call alpha's reset
    alpha.super.reset();
    //if you want to call beta's reset 
    beta.super.reset();

  }
}

edited Dec 26 '14 at 13:11

answered Dec 25 '14 at 16:42

sol4me

15,233
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When i am trying to run the above code with `@override` method then getting error `cannot find symbol @override`. – Manohar Kumar Dec 26 '14 at 05:20
@ManoharKumar `@Override` is with a capital O. – 11684 Dec 26 '14 at 10:31
So to call the alpha version of `reset()` method what statement we have to use in the `@Override public void reset(){ }` code. – Manohar Kumar Dec 26 '14 at 13:08

score 1 · Answer 2 · answered Dec 25 '14 at 17:23

1

In effect,these two methods are the same in the class that implements them.If you try to implement the two methods in Intellij for instance, you only get one method. You can't declare the two even if you want to have different signatures for both of them.

answered Dec 25 '14 at 17:23

Ojonugwa Jude Ochalifu

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What happens, if two interfaces contain the same default method?

2 Answers2