java applet例子---跟踪图片对象的加载
用java.awt包中的MediaTracker跟踪一个Image对象的装载，可以保证所有图片都加载完毕。
package applet;import java.applet.Applet;import java.awt.Button;import java.awt.Graphics;import java.awt.Image;import java.awt.MediaTracker;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.net.MalformedURLException;import java.net.URL;public class MyMediaTracker extends Applet implements Runnable, ActionListener {Button loadB;Thread runner;MediaTracker tracker;Image im1, im2;boolean bothok = false;@Overridepublic void run() {Object[] errArray;tracker = new MediaTracker(this);System.out.println("codeBase:"+this.getCodeBase());try {//this.getCodeBase()是.../java项目名称(此applet所在的java项目)/bin/im1 = this.getImage(new URL(this.getCodeBase(),"jiangnan.jpg"));im2 = this.getImage(new URL(this.getCodeBase(),"happiness.jpg"));} catch (MalformedURLException e) {e.printStackTrace();}tracker.addImage(im1, 0);tracker.addImage(im2, 0);try {tracker.waitForID(0);} catch (InterruptedException e) {e.printStackTrace();}if(tracker.checkAll()){System.out.println("checkAll() is true");}else{System.out.println("checkAll() is false");}if(tracker.isErrorAny()){System.out.println("There is error in Tracker!");if((tracker.statusAll(false)&MediaTracker.ERRORED)!=0){System.out.println("图片在加载过程中出现错误");}else {System.out.println("图片在加载过程中没有出现错误");}if((tracker.statusAll(false)&MediaTracker.ABORTED)!=0){System.out.println("图片在加载过程中被中断");}else {System.out.println("图片在加载过程中没有被中断");}if((tracker.statusAll(false)&MediaTracker.COMPLETE)!=0){System.out.println("图片已被加载完成");}else {System.out.println("图片没有被加载完成");}if((tracker.statusAll(false)&MediaTracker.LOADING)!=0){System.out.println("图片还在加载中");}else {System.out.println("图片未在加载中");}errArray = tracker.getErrorsID(0);for(int i = 0;i<errArray.length;i++){if(errArray[i]==im1){System.out.println("图片1发生错误");}if(errArray[i]==im2){System.out.println("图片2发生错误");}}} //出错else {System.out.println("没有发生错误");}repaint();bothok = true;}@Overridepublic void actionPerformed(ActionEvent e) {if(e.getSource() ==loadB){if(runner ==null){runner = new Thread(this);runner.start();}}}public void init(){loadB = new Button("load");loadB.addActionListener(this);this.add(loadB);}public void paint(Graphics g) {if (bothok) {g.drawImage(im1, 20, 70, this);g.drawImage(im2,400, 50, this);}}}