Graphics and JVMs

[T H Lim]

I have written this small test code to show the difference in the graphical output of 2 different JVMs i.e. Apple JDK 1.5.0 and Windows JDK 1.5.0_13. When I execute this code in Apple JVM, I can see the message "Hi There" quite clearly. Whereas, in Windows JVM, the message is harder be seen if I set Thread.sleep to 100. If I increase the sleep period, I could see a blinking "Hi There" message. Is this has to do with the way I have written the code (probably, I am missing something here) or the JVMs implementation? Either way, how can make this work the way I wanted it? Please advise. Thanks.

    
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
 

    public class TestRandomBoxes extends JFrame {
        private Random pointRandomizer = new Random();
 
        public TestRandomBoxes() {
 
            final JPanel p = new JPanel() {
                @Override
                public void paint(Graphics g) {
                    g.setColor(getBackground());
                    g.fillRect(0, 0, 200, 200);
                    g.setColor(Color.BLACK);
                    g.fillRect(50 + randomPoint().x, 50 + randomPoint().y, 50, 50);
 
                    drawMessage(getParent(), "Hi There");
                }
            };
            p.setPreferredSize(new Dimension(200, 200));
 
            Thread animator = new Thread() {
                @Override
                public void run() {
                    while (true) {
                        p.repaint();
                        try {
                            Thread.sleep(100); // reduce to increase update speed
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            };
            animator.start();
 
            getContentPane().add(new JScrollPane(p));
        }
 
        private void drawMessage(Container c, String message) {
            if (message.length() < 1) {
                return;
            }
 
            Graphics g = c.getGraphics();
            int w = g.getFontMetrics().stringWidth(message) + 10;
            int h = g.getFontMetrics().getHeight() + 4;
 
            g.setColor(new Color(0x33, 0xFF, 0xFF, 50));
            g.fillRect(5, 5, w, h);
            g.setColor(new Color(0x33, 0xFF, 0xFF));
            g.drawRect(5, 5, w, h);
            g.setColor(Color.BLACK);
            g.drawString(message, 8, (5 + h - 4));
        }
 
        private Point randomPoint() {
            return new Point(pointRandomizer.nextInt(50),
                pointRandomizer.nextInt(50));
        }
 
        public static void main(String[] args) {
            TestRandomBoxes sl = new TestRandomBoxes();
            sl.setVisible(true);
            sl.pack();
            sl.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            sl.setBounds(600,450, 100, 100);
        }
}

[Craig Wood]

import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
 
public class TRB extends JFrame {
    private Random pointRandomizer = new Random();
    Point point = new Point();
 
    public TRB() {
        final JPanel p = new JPanel() {
            @Override
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                // These next two lines and the first line
                // (super.paintComponent(g)) do the same thing.
                //g.setColor(getBackground());
                //g.fillRect(0, 0, getWidth(), getHeight());
                g.setColor(Color.BLACK);
                g.fillRect(50 + point.x, 50 + point.y, 50, 50);
 
                String message = "Hi There";
                int w = g.getFontMetrics().stringWidth(message) + 10;
                int h = g.getFontMetrics().getHeight() + 4;
 
                g.setColor(new Color(0x33, 0xFF, 0xFF, 50));
                g.fillRect(5, 5, w, h);
                g.setColor(new Color(0x33, 0xFF, 0xFF));
                g.drawRect(5, 5, w, h);
                g.setColor(Color.BLACK);
                g.drawString(message, 8, (5 + h - 4));
            }
        };
        p.setPreferredSize(new Dimension(200, 200));
 
        Thread animator = new Thread() {
            @Override
            public void run() {
                while (true) {
                    point.setLocation(randomPoint());
                    p.repaint();
                    try {
                        Thread.sleep(1000); // reduce to increase update speed
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        animator.start();
 
        getContentPane().add(new JScrollPane(p));
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(400,400);
        setLocation(200,200);
        setVisible(true);
    }
 
    private Point randomPoint() {
        return new Point(pointRandomizer.nextInt(50),
                         pointRandomizer.nextInt(50));
    }
 
    public static void main(String[] args) {
         new TRB();
    }
}

[T H Lim]

I would prefer the message outside of JPanel. I want the message to be on top of the JPanel. After listening to the kind advices given, this is what I come up with.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JViewport;
 

    public class TestRandomBoxes extends JFrame {
        private Random pointRandomizer = new Random();
 
        public TestRandomBoxes() {
 
            final JPanel p = new JPanel(){
                @Override
                public void paintComponent(Graphics g) {
                    g.setColor(getBackground());
                    g.fillRect(0, 0, 200, 200);
                    g.setColor(Color.BLACK); 
                    g.fillRect(50 + randomPoint().x, 
                        50 + randomPoint().y, 50, 50);
                }
            };
            p.setPreferredSize(new Dimension(200, 200));
 
            final JViewport viewport = new JViewport() {
                @Override
                public void paint(Graphics g) {
                    super.paint(g);
                    int x=50;
                    int y=50;
                    String message = "Hi! There";
                    
                    int w = g.getFontMetrics().stringWidth(message)
                      + 10 ;
                    int h = g.getFontMetrics().getHeight() + 4;
                    
                    g.setColor(new Color(0x33, 0xFF, 0xFF, 50));
                    g.fillRect(x, y, w, h);
                    g.setColor(new Color(0x33, 0xFF, 0xFF));
                    g.drawRect(x, y, w, h);
                    g.setColor(Color.BLACK);
                    g.drawString(message, x, y + h - 4);
                    
                    /* double buffering method   
                    Image bufferImage = createImage(w + 1, h + 1);
                    Graphics buffer = bufferImage.getGraphics();
                    buffer.setColor(new Color(0x33, 0xFF, 0xFF, 50));
                    buffer.fillRect(0, 0, w, h);
                    buffer.setColor(new Color(0x33, 0xFF, 0xFF));
                    buffer.drawRect(0, 0, w, h);
                    buffer.setColor(Color.BLACK);
                    buffer.drawString(message, 0, h - 4);
                    
                    g.drawImage(bufferImage, x, y, null);
                    buffer.dispose();
                    */
                }
            };
            viewport.add(p);
            JScrollPane scrollPane = new JScrollPane();
            scrollPane.setViewport(viewport);
 
            getContentPane().add(scrollPane);
 
            Thread animator = new Thread() {
                @Override
                public void run() {
                    while (true) {
                        repaint();
                        try {
                            Thread.sleep(100);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            };
            animator.start();
        }
        
        private void drawMessage(Graphics g, String message) {
            int w = g.getFontMetrics().stringWidth(message) + 10;
            int h = g.getFontMetrics().getHeight() + 4;
 
            g.setColor(new Color(0x33, 0xFF, 0xFF, 50));
            g.fillRect(5, 5, w, h);
            g.setColor(new Color(0x33, 0xFF, 0xFF));
            g.drawRect(5, 5, w, h);
            g.setColor(Color.BLACK);
            g.drawString(message, 8, (5 + h - 4));
        }
 
        private Point randomPoint() {
            return new Point(pointRandomizer.nextInt(50),
                pointRandomizer.nextInt(50));
        }
 
        public static void main(String[] args) {
            TestRandomBoxes sl = new TestRandomBoxes();
            sl.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            sl.setBounds(600,450, 100, 100);
            sl.validate();
            sl.setVisible(true);
        }
}