[求助]这段代码怎么调

package com.wy.ch6;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class tcmd extends MIDlet implements CommandListener{  //提示tcmd错误但是能编译，却不能执行键盘工能

    private Display dis;
    
    private Form f;
    
    private Command cmd1,cmd2,cmd3;
    
    public tcmd() {
        // TODO Auto-generated constructor stub
        
        dis=Display.getDisplay(this);
        
        f=new Form("测试");
        
        cmd1=new Command("退出",Command.EXIT,1);
        
        cmd2=new Command("帮助",Command.HELP,2);
        
        cmd3=new Command("返回",Command.BACK ,2);
        
        f.addCommand(cmd1);
        
        f.addCommand(cmd2);
        
        f.addCommand(cmd3);
        
        f.setCommandListener(this);
        
    }

    public void destroyApp(boolean arg0) throws MIDletStateChangeException {
        // TODO Auto-generated method stub

    }

    public void pauseApp() {
        // TODO Auto-generated method stub

    }

    public void startApp() throws MIDletStateChangeException {
        // TODO Auto-generated method stub
        
        dis.setCurrent(f);

    }

    public void commandAction(Command command,Display displayable){//这段代码不能执行
        
        if (command.getLabel().equals("帮助")){
            
            System.out.println("帮助");
        }
        
        if (command.getLabel().equals("退出")){
            
            System.out.println("退出");
        }
        
        if (command==cmd3){
            
            System.out.println("返回");
        }
    }
    
}

[ 本帖最后由 sun_life 于 2008-6-3 21:17 编辑 ]