求助 程序 错在哪里？怎么改

import java.awt.event.*;
import java.awt.*;
public class AdapterCounter extends Frame{
    private Button button=new Button("1");
   
    public AdapterCounter(String title){
        super(title);
        //把MyMouseListener的实例注册为Button的监听器
        button.addMouseListener(new MyMouseListener(2));
        
        addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent evt){
                System.exit(0);//结束程序
            }
        });
        
        add(button);
        setSize(100,100);
        setVisible(true);
    }
    public static void main(String[] agrs){
        new AdapterCounter("Hello");
    }
}

class MyMouseListener extends MouseAdapter{
    private int step;        //决定Button上的标号每次增加的步长
    public MyMouseListener(int step){
        this.step=step;
    }
   
    public void mousePressed(MouseEvent evt){
        Button button=(Button)evt.getSource();
        int count=Integer.parseInt(button.getLabel());
        //把Button上的标号加step
        button.setLabel(new Integer(step+count).toString());
    }
}