Drawing Images

// ImagePlacer 

import java.applet.*;
import java.awt.*;

/**
 * ImagePlacer class uses a simple double buffering technique and event handling
 * There is also deliverImage() method providing image delivery for applets
 * and applications with MediaTracker class
 * To transform this applet into an application just change class inheritance

 public class ImagePlacer extends Frame

 * and run it from a command line: java ImagePlacer

 * @author Jeff Zhuk
 */

public class ImagePlacer extends Applet
{
    public static String imageFile = "jar.gif";
    private Image image, offScreenImage = null;
    private Graphics offScreenGraphics = null;
    private int w=0, h=0; // image size
    private int last_x = 30;
    private int last_y = 30;

/**
 *  init() method is called by JVM of Web browser when applet is loaded
 */
    public void init() {
        image = deliverImage(this, imageFile);
    }            
/**
* deliver an image based on a string with URL
* @param iComponent to which image should be delivered
* @param iString fileName
* @return image or null
* @@ author Jeff Zhuk
**/
    public static Image deliverImage(Component iComponent, String iName) {
        MediaTracker tracker = new MediaTracker(iComponent);
        Image image = null;
        try {
            if(iComponent instanceof Applet) {
                Applet applet = (Applet)iComponent;
                image = applet.getImage(applet.getCodeBase(), iName);            
            } else {                
                image = Toolkit.getDefaultToolkit().getImage(iName);
            }                
            tracker.addImage(image,0);
            tracker.waitForID(0);
        } catch (Exception e) {
            System.out.print("deliverImage failure: " + e);
            return null;
        }
        if(tracker.isErrorID(0)) {
            System.out.print("deliverImage failure for " + iName);
            return null;
        }
        return image;
    } 
/**
* Overriding update() method we make painting faster.
* Regular update() method clears screen before painting
* Our version skips clearing the screen and directly calls paint()
* Reminder: update() method is called by JVM to redraw the window
*
* @param g graphics to draw on
**/
    public void update(Graphics g)
    {
        if(image == null)
            return;       // to avoid NullPointerException
        if(offScreenImage == null) { // create offScreenImage for future use
            w = image.getWidth(this);
            h = image.getHeight(this);
            offScreenImage = this.createImage(w, h);
            offScreenGraphics = offScreenImage.getGraphics();
            offScreenGraphics.drawImage(image, 0, 0, null);
        }
        paint(g);
    }
/**
* Drawing happens here
*
* @param g graphics to draw on
**/
    public void paint(Graphics g)
    {
        g.drawString("Click below to place a picture...", 30,30);
            
        if(offScreenImage != null)
            g.drawImage(offScreenImage, last_x, last_y, this);
    }
/**
* Event handler of JDK1.0 called by JVM when MOUSE_UP event happens 
* It is used to draw image at mouse click location
* Writing in JDK1.1 you'll need this.addMouseListener(new MouseListener) { ...
*
* @param e event structure
* @param coordinate x
* @param coordinate y
**/
    public boolean mouseUp(Event e, int x, int y) // JDK 1.0
    {
         // clean previous picture
         Graphics g = this.getGraphics();
         g.setColor(this.getBackground());   // fill rect with bgcolor
         g.fillRect(last_x, last_y, w, h);
         last_x=x;  // get a new mouse position
         last_y=y;
         repaint();
         return true;
    }
}