exercise14_15.java

Introduction to java programming 一书中所有编程练习部分的源码

// Exercise14_15.java: Display an image in different sizes
import javax.swing.*;
import java.awt.*;
import java.net.URL;

public class Exercise14_15 extends JApplet {
  private Image image;

  public void init() {
    // Get the URL for the file name
    URL url = this.getClass().getResource("blackTicker.gif");

    // Obtain a Toolkit instance
    Toolkit toolkit = Toolkit.getDefaultToolkit();

    // Get the image
    image = toolkit.getImage(url);
    getContentPane().add(new DisplayImage());
  }

  // Main method
  public static void main(String[] args) {
    // Create a frame
    JFrame frame = new JFrame("Exercise14_15");

    // Create an instance of the applet
    Exercise14_15 applet = new Exercise14_15();

    // Add the applet instance to the frame
    frame.getContentPane().add(applet, BorderLayout.CENTER);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Invoke init() and start()
    applet.init();
    applet.start();

    // Display the frame
    frame.setSize(500, 400);
    frame.setVisible(true);
  }

// Inner class
class DisplayImage extends JPanel implements Runnable {
  private Thread thread = null;

  int width = 300;
  int height = 300;
  int delta = -10;

  public DisplayImage() {
    thread = new Thread(this);
    thread.start();
  }

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

    g.drawImage(image, 0, 0, width, height, this);
    try {
      Thread.sleep(50);
    }
    catch (InterruptedException ex) {
    }

    if (width < 50) {
      delta = 1;
    }
    else if (width > 300) {
      delta = -1;
    }

    width = width + delta;
    height = height + delta;
  }

  public void run() {
    while (true) {
      repaint();
      try {
        thread.sleep(50);
      }
      catch (InterruptedException ex) {
      }
    }
  }
}
}