How add buttons to Jframe from other class

Question

Hi, a have a little problem;)
I want make a JFrame, but i want to add JButtons from other class. Now I have something like that:
My JFrame class:
package windoow;
import javax.swing.*;
import java.awt.*;
public class MyWindow extends JFrame {
       Butt buttons ;
        public Window(String s) {
                 super(s);
                this.setSize(600, 600);
                this.setVisible(true);
                Buttons();
            public void Buttons(){
                setLayout(null);            
               buttons = new Butt();
               buttons.mywindow =this;
} My class with buttons:
package windoow;
import javax.swing.JButton;
public class Butt {
        MyWindow mywindow;
        JButton b1;
        Butt(){
                  b1 = new JButton("Button");
                  b1.setBounds(100,100,100,20);
                  mywindow.add(b1);  
} and i have NullPointerException.
When i try to make new MyWindow in Butt clas i have something like StackOverFlow.
what should i do?

Answer 1

Your null pointer exception is occuring because, in your Butt() constructor, you are calling mywindow.add(b1), but you don't set mywindow until after you call the constructor in the MyWindow::Buttons() method.
And, if you try to create a new MyWindow() in your Butt() constructor, and, assuming that you are calling the MyWindow::Window(String s) method from the MyWindow() constructor (which is not clear from the code fragment you posted), then Butt() calls new MyWindow() which calls Window(String s) which calls Butt() which calls ... and so on, until the stack overflows.
One possible solution ... pass your MyWindow reference into your Butt() constructor as this, as so:
public void Buttons()
   // stuff deleted
  buttons = new Butt( this );
   // stuff deleted
// AND
Butt( MyWindow mw )
   // stuff deleted
  mywindow = mw;
  mywindow.add( b1 ); // b1 created in stuff deleted section  
}Also, I would call setVisible(true) as the last thing I did during the construction of the frame. This realizes the frame, and from that point forward, most changes to the frame should be made on the event thread.
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