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"?

It already does, by inheritance. Whether you so declare it n the new class is up to you. — user207421, Feb 24 '21 at 03:40

score 1 · Accepted Answer · answered Feb 24 '21 at 03:14

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();
}