如何从另一个类调用JFrame？

Question

I have a class that creates a frame.

public class GameDisplay{

....

public void createDisplay(){
    frame=new JFrame(title);
    canvas=new Canvas();
    canvas.setPreferredSize(new Dimension(width,height));
    canvas.setFocusable(false);
    frame.setSize(width,height);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.setResizable(false);
    frame.add(canvas);
    frame.pack();
}
public Canvas getCanvas(){
    return this.canvas;
}

public JFrame getFrame(){
    return frame;
}

If I have another class that would add Panels and Buttons to the frame, how can I add them? I have tried:

GameDisplay g;
Container c;
c = g.getFrame().getContentPane();

But it returns NullPointer Error. Thus, I can't seem to add panels to it.

Answer 1

Attach your JFrame made in createDisplay() to a static variable. Then access that static variable from another class.

Like this

public static JFrame frame1;

Then in createDisplay()

GameDisplay.frame1 = frame;

In another class to get the content pane just do

c = GameDisplay.frame1.getContentPane();

Hope this helped!