Does a class which is extending an abstract class still has to implement the interface that abstract class is implementing?: java

Question

public abstract class ClassA implements ClassB{
}



public class ClassC extends ClassA implements ClassB{
}

Since class "ClassC" is extending class "ClassA", does "ClassC" still has to implement "ClassB"? Or "ClassB" is automatically implemented for class "ClassC"?

Answer 1

Assuming ClassA is not abstract and fully implements ClassB, then ClassC inherits ClassA's implementation and does not need to re-implement anything from ClassB unless it wants to override the behavior.

It also does not need to specify implements ClassB. The following example is valid:

public static interface I { }
public static class A implements I { }
public static class B extends A { }

public static void main(String[] args) {
    I b = new B();
}