采纳多线程制作动画[Java编程]

import java.awt.*;
import java.applet.*;
//注意到这个程序和Hello程序有什么不一样吗?在这个程序中多了implements Runnable.
public class carton extends Applet implements Runnable
{
Image img;
Thread thd = null;
int i;
int imgWidth = 150;
int imgHeight = 150;
int ncyc=1 ;
String namestr[] = new String[5] ;
//当线程被激活时开始运行run()函数.
public void run()
{
for (int j=0; j<5; j++)
{
namestr[j] = Integer.toString(j,8)+".jpg" ;
}
ncyc = -1 ;
while (true)
{
if (ncyc<=3) ncyc= ncyc+1 ; //初始化循环掌握参数
else ncyc = 0 ;
img = getImage(getCodeBase(), namestr[ncyc]) ;
if (img != null)
{
i=imgHeight;
//repaint();
}
try {Thread.sleep(1000);} catch (InterruptedException e){}
i=0;
while (i<imgHeight)
{
repaint();
try {Thread.sleep(50);} catch (InterruptedException e){}
i+=4;
}
}
}

//每次代码在新位置处重画位图,它都要调用repaint.该函数调用可重载的update办法.update办法与paint办法是相同的,这里为啥不用怕paint(Graphics g)呢?除了paint办法在画图前要排除窗口,而update办法不排除(假如你把update办法改名为paint,你会看到有什么差别).

public void update(Graphics g)
{
if (img != null)
{
g.clipRect(0, 0, imgWidth, i);
g.drawImage(img, 0, i - imgHeight, null);
}
}
public void start()
{
if (thd == null)
{
thd = new Thread(this);
thd.start();
}
}
public void stop()
{
thd = null;
}