default methodで実験

A.java

interface I1 {
    default String id() {
        return "I1";
    }
    default String id1() {
        return id();
    }
}
interface I2 {
    default String id() {
        return "I2";
    }
    default String id2() {
        return id();
    }
}

class C implements I1, I2 {
    public String id() {
        return I1.super.id();
    }
}

public class A {
    public static void main(String[] args) throws Exception {
        C c = new C();
        System.out.println(c.id());
        System.out.println(((I1)c).id());
        System.out.println(((I1)c).id1());
        System.out.println(((I2)c).id());
        System.out.println(((I2)c).id2());
    }
}