lotsofcircles.java

Java程序设计技巧与开发实例附书源代码。

import java.awt.Graphics;
import java.awt.Color;
import java.awt.Image;
import javax.swing.*;

public class LotsOfCircles
        extends JPanel
        implements Runnable
{
    private Image offImage = null;
    private Graphics offGraphics = null;
    private Thread thread = null;
    private int counter = 0;
    private int width = 0, height = 0;
    public LotsOfCircles()
    {
        super();
        setDoubleBuffered(false);
    }

    public void run()
    {
        Thread currentThread = Thread.currentThread();
        while ( (thread == currentThread) && (counter < 10000))
        {
            offPaint(offGraphics);
            counter++;
            if ( (counter % 100) == 0)
            {
                repaint();
            }
            thread.yield();
        }
    }

    public void offPaint(Graphics g)
    {
        Color color = new Color( (int) (255 * Math.random()),
                                (int) (255 * Math.random()),
                                (int) (255 * Math.random()));
        int x = (int) (getSize().width * Math.random());
        int y = (int) (getSize().height * Math.random());
        int r = 10;
        g.setColor(color);
        g.fillOval(x - r, y - r, 2 * r, 2 * r);
    }

    public void initOffImage()
    {
        thread = null;
        width = getSize().width;
        height = getSize().height;
        offImage = createImage(width, height);
        offGraphics = offImage.getGraphics();
        counter = 0;
        thread = new Thread(this);
        thread.start();
    }

    public void paintComponent(Graphics g)
    {
        if ( (width != getSize().width) || (height != getSize().height))
        {
            initOffImage();
        }
        if (offImage != null)
        {
            g.drawImage(offImage, 0, 0, null);
        }
    }
}