关于多线程，请高手指教！

Question

我编写了一个多线程的小应用程序：实现上下两行字符的左右来回移动。
但程序运行时没有任何效果！
程序如下：
import java.awt.*;
import java.applet.*;public class ThreadString extends Applet
{

public void init()
{

Thread thr1=new Thread(new Thread1());
Thread thr2=new Thread(new Thread2());

thr1.start();
thr2.start();

}
}

class Thread1 extends Canvas
implements Runnable
{ int y1;


public void run()
{
while(true)
{
repaint();
try{Thread.sleep(100);}
catch(InterruptedException e){}
}
}
public void paint(Graphics g)
{
if(y1<0)  y1=200; else y1=y1-10;
g.drawString("hello,java!",y1,20);
}
}
class Thread2 extends Canvas
implements Runnable
{
int y2;
public void run()
{
while(true)
{
repaint();
try{Thread.sleep(100);}
catch(InterruptedException e){}
}
}
public void paint(Graphics g)
{
if(y2>200) y2=0; else y2=y2+10;
g.drawString("hello,java!",y2,40);
}
}

Answer 1

import java.awt.*;
import java.applet.*;public class ThreadString extends Applet
{

public void init()
{

Canvas t1=new Thread1(); //实例化画布的同时启动线程
this.add(t1);
Canvas t2=new Thread2();
this.add(t2);
}
}

class Thread1 extends Canvas
implements Runnable
{ int y1;

public Thread1() //添加了构造，用于设定画布大小，并启动线程
{
this.setSize(300,150);
new Thread(this).start();
}
public void run()
{
while(true)
{
repaint();
try{Thread.sleep(100);}
catch(InterruptedException e){}
}
}
public void paint(Graphics g)
{
if(y1<0)  y1=200; else y1=y1-10;
g.drawString("hello,java!",y1,20);
}
}
class Thread2 extends Canvas
implements Runnable
{
int y2;
public Thread2()
{
this.setSize(300,150);
new Thread(this).start();
}
public void run()
{
while(true)
{
repaint();
try{Thread.sleep(100);}
catch(InterruptedException e){}
}
}
public void paint(Graphics g)
{
if(y2>200) y2=0; else y2=y2+10;
g.drawString("hello,java!",y2,40);
}
}

Answer 2

楼上正解，关键是在applet中添加画布并且要设置画布的大小（默认是（0，0））。