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.

You can try multilevel inheritance. – Achintya Jha Mar 29 '13 at 06:45 — Achintya Jha, Mar 29 '13 at 06:45

score 4 · Accepted Answer · answered Mar 29 '13 at 06:45

4

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 
     }  

 }

answered Mar 29 '13 at 06:45

Sudhanshu Umalkar

still it is saying "package a doesnot exists" – Ojas Kale Mar 29 '13 at 07:29
all classes and variables are public. – Ojas Kale Mar 29 '13 at 07:30
still it is saying "package a doesnot exists" – Ojas Kale Mar 29 '13 at 07:46
theres this "rs" variable in main class . i want to acess it in a class name entryform . so as u said i created an object like "main abc = new main() ;" n fr acessinig rs also write rs.abc.moveToInsertRow(); but its showing error – Ojas Kale Mar 29 '13 at 07:48

score 3 · Answer 2 · answered Mar 29 '13 at 06:46

3

Java does not support multiple inheritance, so you can't extend both A and JFrame.

You could either turn A into an interface, or embed an instance of A into B.

answered Mar 29 '13 at 06:46

NPE

score 1 · Answer 3 · answered Mar 29 '13 at 06:46

1

You can do like this :

public class A extends javax.swing.JFrame{

...

}

and then

public class B extends A{

...

}

answered Mar 29 '13 at 06:46

Abubakkar

score 1 · Answer 4 · edited May 23 '17 at 12:08

1

Use composition or aggregation. Learn more about Has-A relationship.

Read this and this

edited May 23 '17 at 12:08

Community

answered Mar 29 '13 at 06:48

AmitG

rai.skumar · Answer 5 · 2016-07-05T05:28:25.880

Multiple Inheritance is NOT supported in Java. But still Java provides other ways to achieve multiple inheritance.

Check if you can solve it by using interface, as you can implement multiple interfaces.
Use composition or aggregation. Fundamentally, we achieve code re-usability using inheritance. The same can be achieved using composition/aggregation as well.
Use Inner classes (you can extend multiple classes using inner classes)

score 1 · Answer 6 · answered Mar 29 '13 at 07:31

1

Make class A an interface and B implementing it like this :

public interface A{
public ....[Variables] 
}

public class B extends javax.swing.JFrame implements A{
   ...
}

answered Mar 29 '13 at 07:31

RE60K

6 Answers6