Information About Implementing Interfaces

The code in the questionnaire that eliminates the compilation error with as much intention as possible is as follows:

public interface a{
    default void sample() {
        System.out.print("A");
    }
}

public interface extensions a{

}

public class components b{
    @ Override
    public void sample() {
        b.super.sample();
        System.out.print("java");
    }
}

public class Main {
    public static void main(String[]args) {
        aa = new c();
        a.sample();
    }
}

If you answer on the assumption that the actual code you are expecting is the one above,

b class implements a, but does not implement sample() I think it's the wrong class to implement the interface, but I have no compilation errors and I'm wondering.

First, b is an interface, not a class.
Also, even if b is a class that implements a, sample() is implemented by default on the a interface, so implementation in b can be omitted.

Therefore,

Please let me know if it is possible without implementing sample() in the b class.

The answer to is yes.

Class implementing the interface must implement the declared method.

For , the default method was introduced in Java 8.
If the default method provides a default implementation, override is no longer required on the implementation class side.

• The Java® Language Specification Java SE 8 Edition>Chapter 9.Interfaces>9.4.Method Declarations

A default method(snip)provides a default implementation for any class that implements the interface without overriding the method.