JPanel paintComponent()

[stevanity]

Im reading Core Java (Cay Horstmann) V I

And I came across this program.........

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

class MyFrame extends JFrame
{
	private ButtonPanel buttonPanel;
	public MyFrame()
	{
		setSize(300,200);
		setLocation(570,350);
		setTitle("Button Test");
		
		buttonPanel=new ButtonPanel();
		add(buttonPanel);
	}

	private class ButtonPanel extends JPanel
	{
		public void paintComponent(Graphics g)
		{
			JButton redButton=new JButton("Red");
			JButton yellowButton=new JButton("Yellow");
			JButton greenButton=new JButton("Green");
			
			add(redButton);
			add(yellowButton);
			add(greenButton);
			
			ColorAction setRed=new ColorAction(Color.RED);
			ColorAction setYellow=new ColorAction(Color.YELLOW);
			ColorAction setGreen=new ColorAction(Color.GREEN);
			
			redButton.addActionListener(setRed);
			yellowButton.addActionListener(setYellow);
			greenButton.addActionListener(setGreen);
		}
	}
	
	private class ColorAction implements ActionListener
	{
		private Color bgColor;
		
		public ColorAction(Color c)
		{
			bgColor=c;
		}
		
		public void actionPerformed(ActionEvent e)
		{
			buttonPanel.setBackground(bgColor);
		}
	}
}
		
class JButtonTest
{
	public static void main (String arg[])
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				MyFrame buttonFrame=new MyFrame();
				buttonFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				buttonFrame.setVisible(true);
			}
		} );
	}
}

But I modified it. I created a new InnerClass for the button panel and drew the buttons using the paintComponent method. But in that book, they directly created an instance for JPanel in the Frame class itself and added buttons directly from constructor of the Frame class.

When I executed my code, I got three buttons and when I clicked a button, the BG color didnt change and instead the image of the button was drawn in the top left corner.

So where am I going wrong?

[javaAddict]

I tested your code and couldn't get it to work. The buttons weren't displayed.
I would advise you not to use the paintComponent. It it used to paint graphics (circles, images, lines, ....)
You don't need that method to add buttons and other components such as JLabels

Try putting the code of the ButtonPanel in a constructor:

....
....
	private class ButtonPanel extends JPanel
	{
            public ButtonPanel() {
                JButton redButton=new JButton("Red");
                JButton yellowButton=new JButton("Yellow");
                JButton greenButton=new JButton("Green");
                
                add(redButton);
                add(yellowButton);
                add(greenButton);
                
                ColorAction setRed=new ColorAction(Color.RED);
                ColorAction setYellow=new ColorAction(Color.YELLOW);
                ColorAction setGreen=new ColorAction(Color.GREEN);
                
                redButton.addActionListener(setRed);
                yellowButton.addActionListener(setYellow);
                greenButton.addActionListener(setGreen);
            }
                /*
		public void paintComponent(Graphics g)
		{
			
		}
                */
	}
....
....

[NormR1]

Why are you adding components in the paintComponent method? That method can be called many times a second to do a repaint.

Also your paintComponent doesn't do any painting?