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Thread: Simple swing GUI code....Plz help

  1. #1
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    Default Simple swing GUI code....Plz help

    I am learning java swing programming and have a problem.
    I want to create simple Bouncing ball application using threading and swing..
    So, I created a JFrame and placed 2 buttons, start and stop, and placed a simple ball using fillOval().
    Here is the code...




    package bouncingball;
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    class Ball extends JPanel
    {
    @Override
    public void paintComponent(Graphics g)
    {
    g.setColor(Color.red);
    g.fillOval(20, 20, 100, 100);
    }
    }

    public class BouncingBall {

    JFrame f;
    JButton start, stop;

    BouncingBall()
    {
    f = new JFrame("BouncingBall");
    f.setLayout(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setSize(700, 700);
    f.getContentPane().add(new Ball());
    start = new JButton("START");
    start.setBounds(100, 450, 150, 20);
    f.getContentPane().add(start);
    stop = new JButton("STOP");
    stop.setBounds(100, 500, 150, 20);
    f.getContentPane().add(stop);
    f.setVisible(true);

    }

    public static void main(String[] args) {
    // TODO code application logic here
    BouncingBall b = new BouncingBall();
    }
    }


    I set the layout to null. On running this code, buttons are visible, but ball is not.
    I know that in layout, we can add only one thing to each region. But, since setLayout(null), what is wrong with it?


  2. #2
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    Default Re: Simple swing GUI code....Plz help

    The natural size of a JPanel is like 0,0 or something. So you just cannot see the Ball JPanel.

    The easiest way to do this would be to make the Ball JPanel your content pane. To do that, change this:
    f.getContentPane().add(new Ball());
    to this:
    f.setContentPane(new Ball());

    I think that should do it.
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    Arati2512 (April 13th, 2012)

  4. #3
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    Default Re: Simple swing GUI code....Plz help

    You are using a null layout - all components added must be given a defined size, which the Ball panel has not been given. That being said, I recommend against using a null layout - Layouts make your life so much easier in the long run, and make your application much more portable across computers and systems. They may seem daunting at first, but a little time playing with them, nesting them, etc...can help a lot in the long run.

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