package birdfly;import java.awt.*;import java.awt.event.*;import java.applet.*;/** * <p>Title: 飛行的大鳥</p> * <p>Description: 在沙漠中飛行的大鳥</p> * <p>Copyright: Copyright (c) 2004</p> * <p>Company: 北京師范大學(xué)計算機系</p> * @author 孫一林 * @version 1.0 */public class BirdFly extends MultiThreadApplet {  boolean isStandalone = false;  Image offScreenImg;					//存放備用屏幕的內(nèi)容  Graphics offScreenG;					//備用屏幕的繪圖環(huán)境  MediaTracker tracker;					//媒體跟蹤器  Image walkerImgs[]=new Image[4];		//存放大鳥走路姿勢圖像  Image currentImg;						//當前放映的大鳥動作圖像  int xpos,ypos=0;						//大鳥動作圖像顯示的位置  int walk_step=20;						//大鳥圖像每次移動的距離  int delay = 250;						//每幀時延（毫秒）  Image bgImage;						//存放草原背景圖像  int applet_width,applet_height;  int birdImg_width;						//大鳥圖像寬度  //Get a parameter value  public String getParameter(String key, String def) {    return isStandalone ? System.getProperty(key, def) :      (getParameter(key) != null ? getParameter(key) : def);  }  //Construct the applet  public BirdFly() {  }  //Initialize the applet  public void init() {    try {      jbInit();    }    catch(Exception e) {      e.printStackTrace();    }  }  //Component initialization  private void jbInit() throws Exception {    tracker = new MediaTracker(this);    for (int i=0;i<walkerImgs.length;i++){					//獲取大鳥動作圖像      walkerImgs[i]=getImage(getCodeBase(),"images/bird"+i+".gif");      tracker.addImage(walkerImgs[i], 0);				//列入0組跟蹤范圍    }    bgImage = getImage(getCodeBase(),"images/"+"bg.gif");	//獲取草原背景圖像    tracker.addImage(bgImage, 0);						//列入0組跟蹤范圍    applet_width = getSize().width;    applet_height = getSize().height;    try {      offScreenImg = createImage (applet_width,applet_height);//創(chuàng)建備用屏幕      offScreenG = offScreenImg.getGraphics ();//獲取備用屏幕的繪圖環(huán)境    }    catch (Exception e) {      offScreenG = null;		//若出錯，就置備用屏幕的繪圖上下文環(huán)境為null    }  }  public void run(){    try{      tracker.waitForID(0);			//等待0組中所有圖像的到達    }    catch(InterruptedException e){      return;    }    birdImg_width=walkerImgs[0].getWidth(this);    int i=0;    while(true){      for(xpos=-birdImg_width;xpos<=applet_width;xpos+=walk_step){//計算位置        currentImg=walkerImgs[i];        repaint();        i=(i+1)%walkerImgs.length;			//計算下一幀是哪幅圖像        try{          Thread.sleep(delay);        }        catch(InterruptedException e){        }      }    }  }  public void paint(Graphics g){    g.drawImage(bgImage,0,0,this);    g.drawImage(currentImg,xpos,ypos,this);  }  public void update(Graphics g){    if (offScreenG!=null) {					//如果備用屏幕創(chuàng)建成功      paint(offScreenG);      g.drawImage(offScreenImg,0,0,this);	//將備用屏幕內(nèi)容畫到當前屏幕來    }    else{      paint(g);    }  }  //Get Applet information  public String getAppletInfo() {    return "飛行的大鳥";  }  //Get parameter info  public String[][] getParameterInfo() {    return null;  }}