Re: JPanel Background problem....

From:
Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>
Newsgroups:
comp.lang.java.help
Date:
Mon, 04 Feb 2008 08:14:44 -0800
Message-ID:
<47a739c1$0$3042$7836cce5@newsrazor.net>
TheBigPJ wrote:

My code compiles fine, however it doesn't do as its told to put it
lightly.

I'm attempting to set the "JPanel Pork" to be yellow initially. Then
change it via JButtons later.

What am I doing wrong? It wont initially set to yellow.

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

public class Initial_Displaying extends JFrame
{
    private The_Meat Pork;

    public Initial_Displaying()
    {
           Pork = new The_Meat();
    }

        public void initComponents() throws Exception {

        Pork.setBackground(Color.yellow); // It doesnt set it to
yellow :(

        JPanel content = new JPanel();
        content.setLayout(new BorderLayout(5, 5));
        content.add(Pork, BorderLayout.WEST);

        setContentPane(content);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setTitle("Initial Displaying");
        setLocationRelativeTo(null); // Center window.
        pack();
        setVisible(true);
    }

    static public void main(String[] args) { // Main
entry point
        try {
         Initial_Displaying Test = new Initial_Displaying();
         Test.initComponents();
        }
    catch (Exception e) {
        e.printStackTrace();
        }
    }
}

----------------------------------
import java.awt.*;
import javax.swing.*;
import java.awt.Graphics;
import java.awt.Graphics2D;

public class The_Meat extends JPanel
{
    private Color BackGroundColour;

    public The_Meat()
    {
        setPreferredSize(new Dimension(250,250));
    }

    public void paintComponent(Graphics g){
        paintComponent((Graphics2D) g);
        }//paintComponent

    public void paintComponent(Graphics2D g){

        g.drawLine(50,50,50,150);
        g.drawLine(50,100,100,100);
        g.drawLine(100,50,100,100);
        g.drawLine(50,50,100,50);
        g.drawLine(150,50,200,50);
        g.drawLine(175,50,175,150);
        g.drawLine(175,150,150,150);
        g.drawLine(150,150,150,125);

        g.setFont(new Font("Courier New", Font.PLAIN, 24));
        g.drawString("PJ",10,25);

        g.drawRect(5,5,35,25);
        g.drawRect(40,40,170,120);

        g.drawLine(5,5,40,40);
        g.drawLine(5,30,40,160);
        //g.drawLine( Needs to show that the second square is actually
filled.
        g.drawLine(40,5,210,40);

        }//paintComponent
}


A couple of comments on style, and then hopefully an answer for you.

The_Meat isn't a good name for a class. TheMeat is perfectly acceptable
from a convention point of view. It might even be better if you simply
call it Meat. Also, "Pork" isn't a good variable name, "pork" would be
better.

Hopefully the answer you need:
I believe the background of a panel is only painted if the opaque
property is set (setOpaque(true);)
9
Try that first. If that doesn't work, try:
Paint p = g.getPaint();
g.setColor(getBackground());
g.fillRect(getVisibleRect());
g.setPaint(p);

Oh, and BTW, any time you interact with Swing code, you should do the
interaction on the Event Dispatch Thread. Any heavy work you do should
be offloaded to a worker thread.
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>

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