Mutilple inheritance strange behavior - Java 8

In the following code if I uncomment I3 and implements I2 and I3 then there is a compilation failure with the following error:

unrelated defaults for m2() from I3 and I2

Which is as fine and expected behavior.

However, when I replace I3 with I, it compiles successfully and I am getting I2 as output.

public class DefaultMethodTest implements I, I2 {
    public static void main(String[] args) {
        DefaultMethodTest obj = new DefaultMethodTest();
        obj.m2();
     }
}
    
interface I {
        default void m2() {
        System.out.println("I1");
    }
}

interface I2 extends I {
        default void m2() {
        System.out.println("I2");
    }
}

//interface I3 extends I {
//
//    default void m2() {
//        System.out.println("I3");
//    }
//}

Now I have couple of questions here :

• Why there is no compilation failure in second case although both interface have same default method m2?

• Why I2 got precedence over I ?.

Note: This question is not related to java-8-default-method-inheritance

As per the default method resolution rules, the default method in the most specific default providing interface will be chosen. In your case, both I and I2 has a default method (each) with the same signature. Hence, it will choose I2 which is your most specific default providing interface.

On the other hand, if you implement I2, I3, there will be conflict that you need to resolve (by implementing m2 in your class).

References:

http://www.lambdafaq.org/how-are-conflicting-method-declarations-resolved/ https://javadevcentral.com/default-method-resolution-rules