Inheritance in Java: Extending another class when I've already extended one

Question

I have to extend class A's variables into Class B. For that I have to write:

public class B extends class A

But in my case, the place is already taken up by "extends javax.swing.JFrame". It looks like:

public class B extends javax.swing.JFrame

Please suggest any method to inherit variables from class A to class B. I am very new to this field. So please explain.

Answer 1

Either use composition or create an inner class in class B which extends class A.

 class B extends JFrame {
     A a = ... // this is one option

     class C extends A {
         // this is another option 
     }  

 }