Mega Code Archive
Proxy pattern in Java
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/*
The Design Patterns Java Companion
Copyright (C) 1998, by James W. Cooper
IBM Thomas J. Watson Research Center
*/
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Label;
import java.awt.MediaTracker;
import java.awt.Toolkit;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class ProxyDisplay extends JFrame {
public ProxyDisplay() {
super("Display proxied image");
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
JPanel p = new JPanel();
getContentPane().add(p);
p.setLayout(new BorderLayout());
ImageProxy image = new ImageProxy("elliott.jpg", 321, 271);
p.add("Center", image);
p.add("North", new Label(" "));
p.add("West", new Label(" "));
setSize(370, 350);
setVisible(true);
}
static public void main(String[] argv) {
new ProxyDisplay();
}
}
//==================================
class ImageProxy extends JPanel implements Runnable {
int height, width;
MediaTracker tracker;
Image img;
JFrame frame;
Thread imageCheck; //to monitor loading
public ImageProxy(String filename, int w, int h) {
height = h;
width = w;
tracker = new MediaTracker(this);
img = Toolkit.getDefaultToolkit().getImage(filename);
tracker.addImage(img, 0); //watch for image loading
imageCheck = new Thread(this);
imageCheck.start(); //start 2nd thread monitor
//this begins actual image loading
try {
tracker.waitForID(0, 1);
} catch (InterruptedException e) {
}
}
public void paint(Graphics g) {
if (tracker.checkID(0)) {
height = img.getHeight(frame); //get height
width = img.getWidth(frame); //and width
g.setColor(Color.lightGray); //erase box
g.fillRect(0, 0, width, height);
g.drawImage(img, 0, 0, this); //draw loaded image
} else {
//draw box outlining image if not loaded yet
g.setColor(Color.black);
g.drawRect(1, 1, width - 2, height - 2);
}
}
public Dimension getPreferredSize() {
return new Dimension(width, height);
}
//public int getWidth() {return width;}
//public int getHeight(){return height;}
public void run() {
//this thread monitors image loading
//and repaints when done
//the 1000 msec is artifically long
//to allow demo to display with delay
try {
Thread.sleep(1000);
while (!tracker.checkID(0))
Thread.sleep(1000);
} catch (Exception e) {
}
repaint();
}
}
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