interface and inheritance in java

Question

I have a question of how to relate interface to inheritance, for example:

if class A implements interface X, also class A is the superclass of class B and class C, my question is , does it mean both class B and class c will automatically implement interface X as well?

Answer 1

It depends if class A is an abstract class or not. Assuming that class A fully implements interface X then both B and C will implement X. For example each line of code would be perfectly fine...

X one = new A();
X two = new B();
X three = new C();

Answer 2

if class A implements interface X, also class A is the superclass of class B and class C, my question is , does it mean both class B and class c will automatically implement interface X as well?

Not if A has an implementation. Otherwise, yes they need to.

public interface X{ public void stuff();} 

public class A implements X { 
   // A not abstract, must implement "stuff()" 
   // therefore, B and C will automatically have an implementation of "stuff()" too
}

but if A is abstract

public abstract A implements X {
    // not implemented.  B and C will need to implement
    public abstract void stuff(); // not implemented 
}