whirlinglogo.java

非常好的java事例以及带源码事例的java2教程

import java.awt.*;
import java.awt.image.*;
import javax.swing.*;
import java.net.*;
import java.awt.geom.*;                 // For AffineTransform

public class WhirlingLogo extends JApplet
                          implements Runnable
{
  // This method is called when the applet is loaded
  public void init()
  {
    tracker = new MediaTracker(this);
    Image image = null;
    try
    {
      // Image from a file specified by a URL
      image = getImage(new URL(getCodeBase(),"Images/wrox_logo.gif")); 
    }

    catch(MalformedURLException e)
    {
      System.out.println("Failed to create URL:\n" + e);
    }

    tracker.addImage(image,0);

    try
    {
      tracker.waitForAll();                       // Wait for image to load
      if(tracker.isErrorAny())                    // If there is an error
        return;                                   // give up
         
      Dimension size = getSize();                   // Get applet size
      imageWidth = image.getWidth(this);            // Get image width
      imageHeight = image.getHeight(this);          // and its height

      // Calculate scale factor so diagonal of image fits width and height
      double diagonal = Math.sqrt(imageWidth*imageWidth + imageHeight*imageHeight);
      double scaleFactor = Math.min(size.width/diagonal, size.height/diagonal);

      // Create a transform to translate and scale the image
      at.setToTranslation((size.width-imageWidth*scaleFactor)/2,
                          (size.height-imageHeight*scaleFactor)/2);
      at.scale(scaleFactor,scaleFactor);

      imagePanel = new ImagePanel(image);         // Create panel showing the image
      getContentPane().add(imagePanel);           // Add the panel to the content pane
    }

    catch(InterruptedException e)
    {
      System.out.println(e);
    }
  }

  // This method is called when the browser starts the applet
  public void start()
  {
    if(tracker.isErrorAny())                   // If any image errors
      return;                                  // don't create the thread
    whirler = new Thread(this);                // Create the animation thread
    whirler.start();                           // and start it
  }

  // This method is called when the browser want to stops the applet
  // when it's not visible for example
  public void stop()
  {
    whirler = null;                                  // Discard the thread
  }

  // This method is called when the animation thread is started
  public void run()
  {
    long time = System.currentTimeMillis(); // Starting time
    long interval = 50;                    // Time interval msec

    angle = 0;                                          // Initial rotation angle
    double angleIncrement = interval*Math.PI/1000;    // Complete rotation in 2 secs

    // Move image while the whirler thread is running
    while(Thread.currentThread() == whirler)
    {
      imagePanel.repaint();                 // Repaint the image

      // Wait until the end of the next interval
      try
      {
        time += interval;
        angle += angleIncrement%(2*Math.PI);           // Increment the rotation angle
        Thread.sleep(Math.max(0, time - System.currentTimeMillis()));
      }

      catch (InterruptedException e)
      {
        break;
      }
    }
  }


  class ImagePanel extends JPanel
  {
    public ImagePanel(Image image)
    {
      this.image = image;
    }

    public void paint(Graphics g)
    {
       Graphics2D g2D = (Graphics2D)g;
       g2D.transform(at);                                   // Apply scale & translate
       g2D.setPaint(Color.lightGray);                          // Set a background color
       g2D.fillRect(0, 0, imageWidth, imageHeight);            // paint background


       g2D.rotate(angle, imageWidth/2.0, imageHeight/2.0);   // Rotate about center
 
       // draw scaled image with background
       g2D.drawImage(image, 0, 0, this);
    }

    Image image;                                       // The image
  }

  Thread whirler;                // Animation thread
  MediaTracker tracker;          // Tracks image loading
  ImagePanel imagePanel;
  AffineTransform at = new AffineTransform();   
  int imageWidth, imageHeight;   // Image dimensions
  double angle;                  // Rotation angle 

}