barrier.java

Java程序设计(美) David D. Riley著 机械工业出版社 书籍配套 代码

/*	Pylon objects display an image like a plastic highway barrier/cone.
    Author:  David Riley -- Jan, 2005 */
    
/**	class invariant
 *   	getWidth() >= 36  AND  getHeight() >= 36  
 */

import java.awt.Toolkit.*;
import java.awt.*;
import javax.imageio.ImageIO;
import java.io.*;
import javax.swing.JComponent;

public class Barrier extends JComponent implements java.awt.image.ImageObserver {
	private java.awt.Image content;

	/**	pre:    a proper JPEG image file must be in file /graphics/Pylon.jpg in the
     *          same folder as the current .class file
     *  post:   an pylon image is instantiated
     *          and  getX() == 0   and  getY() == 0   
     *          and  getWidth() == 36  AND  getHeight() == 36   
     */
	public Barrier()  {
		super();
		setBounds(0, 0, 36, 36);
        setImage("graphics/Barrier.jpg");
	} 

	/**	post:   Upon repaint the image displayed will be given by the 
     *          file with complete pathname specified as s 
     *          (Note that the file should be a gif or jpeg encoding.)  
     */
	private void setImage(String s)  {
        java.net.URL url = getClass().getResource(s);  // for applets
        if (url == null)   {
            url = getClass().getResource("/"+s);
            if (url == null)
                try {  // for applications
                    content = ImageIO.read(new File(s));
                    System.out.println("hereh");
                } catch(IOException ioe) {
                    ioe.printStackTrace();
                }
            else
                content = getToolkit().getImage(url);
        } else
            content = getToolkit().getImage(url);

	}

	public void paint(Graphics g)  {
		g.drawImage(content, 0, 0, getWidth(), getHeight(), this);
	} 

}