一个java程序，无法运行，不知道哪里出错了，请高手指点？

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
public class Exam5_1 extends Applet implements ActionListener{
Button But1,But2;
int button=0;
public void init(){
But1=new Button("按钮1");
But2=new Button("按钮2");
But1.setActionCommand("but1");//调用setActionCommand()方法指定命令名
But2.setActionCommand("but2");
add(But1);
add(But2);
But1.addActionListener(this);
But2.addActionListener(this);
}
public void paint(Graphics g)
{
if(button==1)
g.drawString("您按了按钮1",10,20);
else if(button==2)
g.drawString("您按了按钮2",10,20);
}
public void actionPerformed(ActionEvent e)
{
if(e.getActionCommand()=="but1")
button=1;
else if(e.getActionCommand()=="but2")
button=2;
repaint();
}
}