draw rectangle in Jpanel

Question

I am trying to get my hands on GUI programming in java and wanted to draw a rectangle in Jpanel. Code does not give any error but I cannot get rectangle in the GUI. Can somebody please tell me what I am missing in the following code. I am sure it is pretty simple so please be gentle.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class HelloWorldGUI2 {

    private static class ButtonHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
        System.exit(0);
        }
        }
    private static class RectDraw extends JPanel {
        public void paintComponent(Graphics g) {
        super.paintComponent(g);  
         g.drawRect(230,80,10,10);  
         g.setColor(Color.RED);  
         g.fillRect(230,80,10,10);  
        }
        }
    public static void main(String[] args) {
        JPanel content = new JPanel();
        RectDraw newrect= new RectDraw();
        JButton okButton= new JButton("OK");
        JButton clearButton= new JButton("Clear");
        ButtonHandler listener= new ButtonHandler();
        okButton.addActionListener(listener);
        clearButton.addActionListener(listener);
        content.add(okButton);
        content.add(clearButton);
        content.add(newrect);
        JFrame window = new JFrame("GUI Test");
        window.setContentPane(content);
        window.setSize(250,100);
        window.setLocation(100,100);
        window.setVisible(true);
        }

    }

Answer 1

Your newrect RectDraw's size is likely going to be quite small, probably [0, 0], since it has been added to a FlowLayout using JPanel and doesn't have a preferredSize set. Consider overriding its getPreferredSize() method and returning a suitable Dimension so that its drawing can be seen.

private static class RectDraw extends JPanel {
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);  
    g.drawRect(230,80,10,10);  
    g.setColor(Color.RED);  
    g.fillRect(230,80,10,10);  
  }

  public Dimension getPreferredSize() {
    return new Dimension(PREF_W, PREF_H); // appropriate constants
  }
}

Also,

• The paintComponent method should be protected, not public
• Don't forget to use @Override before your method overrides.
• Aim for much less code in the main method and more code in the "instance" world, not the static world.
• Take care with your code formatting. Poor code formatting, especially misleading indentations, leads to silly errors.