Setting panel color in different places produces different effects.

[shall]

The only way I have found to change the panel color is to fill it will a color. However, it depends in what part of the program I perform that action. For example, if I do it in the paintComponent member function it changes the panel color. However, if I do it in my main function, it doesn't change the panel color. Is there another way to change the panel color? I tried setting the foreground color and that doesn't work.

Example 1: Using paintComponent member function to change panel color

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PaintPanelBackGround extends JPanel
{

    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        Graphics2D g2d = (Graphics2D) g;

        g2d.setColor(Color.WHITE);

        g2d.fillRect(0,0,800,800);        
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args)
    {
        final PaintPanelBackGround panel = new PaintPanelBackGround();

        JFrame frame = new JFrame("CaptureImagePosition");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.setSize(800, 800);

        Dimension a = new Dimension();
        a.width = 800;
        a.height = 800;
        panel.setPreferredSize(a);

        frame.setContentPane(panel);

        frame.setVisible(true);
    }
}

Example 2: Using main to change panel color

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PaintPanelBackGround extends JPanel
{

    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        Graphics2D g2d = (Graphics2D) g;

        //this.setForeground(Color.red);

        //g2d.setColor(Color.WHITE);

        //g2d.fillRect(0,0,800,800);        
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args)
    {
        final PaintPanelBackGround panel = new PaintPanelBackGround();

        JFrame frame = new JFrame("CaptureImagePosition");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.setSize(800, 800);

        Dimension a = new Dimension();
        a.width = 800;
        a.height = 800;
        panel.setPreferredSize(a);

        frame.setContentPane(panel);

        frame.setVisible(true);

        Graphics2D g2d = (Graphics2D) frame.getGraphics();

        g2d.setColor(Color.WHITE);

        g2d.fillRect(0,0,800,800);
    }
}

[shall]

Ok, I tried panel.setBackground(Color.white) in main and that changed the panel color to white.

I had thought I tried that before.

[DarrylBurke]

1. Never set the background, foreground or any other attribute in a painting method override.
2. Never use getGraphics() of a Component. Not until (or if ever) you intimately understand the difference between passive and active rendering, and why you don't need the latter.

db

[shall]

Thanks for the info. I haven't heard of those terms before and I didn't know about active rendering.

[DarrylBurke]

You don't really need to know about it. Not in these days of efficient JVMs and fast computers. That's why I said

and why you don't need the latter.

Go through this Lesson: Performing Custom Painting (The Java™ Tutorials > Creating a GUI With JFC/Swing)

db