Implementing two interfaces with two default methods of the same signature in Java 8

Question

Suppose I have two interfaces:

public interface I1
{
    default String getGreeting() {
        return \"Good Morning!\";
    }
}

public interface I2
{
             


        

Answer 1

If a class implements 2 interfaces both of which have a java-8 default method with the same signature (as in your example) the implementing class is obliged to override the method. The class can still access the default method using I1.super.getGreeting();. It can access either, both or neither. So the following would be a valid implementation of C1

public class C1 implements I1, I2{
    public static void main(String[] args)
    {
        System.out.println(new C1().getGreeting());
    }

    @Override //class is obliged to override this method
    public String getGreeting() {
        //can use both default methods
        return I1.super.getGreeting()+I2.super.getGreeting();
    }

    public String useOne() {
        //can use the default method within annother method
        return "One "+I1.super.getGreeting();
    }

    public String useTheOther() {
        //can use the default method within annother method
        return "Two "+I2.super.getGreeting();
    }


}