猜数字游戏,我的第一个J2ME程序,很多问题,有待于解决

import Javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;

/**
 *
 * @author  aoenzh
 * @version
 */
public class Test extends MIDlet implements CommandListener{
   
    private Command cmdOK;
    private Command cmdEXIT;
    private TextField txtInput;
    private Form myForm;
    private int rndNum;
    //private int inputNum;
    Display display;
    public Test(){
       
    }
   
    public void startApp() {
        Random tmpRand=new Random();
        rndNum=tmpRand.nextInt(100);
        txtInput=new TextField("请输入0-50之间的数字","",25,TextField.NUMERIC);
        cmdOK=new Command("确认",Command.SCREEN,1);
        cmdEXIT=new Command("退出",Command.EXIT,1);
        myForm=new Form("猜数字");
        myForm.append(txtInput);
        myForm.addCommand(cmdOK);
        myForm.addCommand(cmdEXIT);
        myForm.setCommandListener(this);
        display =Display.getDisplay(this);
        display.setCurrent(myForm);
    }
   
    public void pauseApp() {
    }
   
    public void destroyApp(boolean unconditional) {
    }
   
    public void commandAction(Command command, Displayable displayable) {
        if(command==cmdEXIT){
            destroyApp(true);
            notifyDestroyed();
        }
        if(command==cmdOK){
            Alert alert = new Alert("猜数字","",null,AlertType.INFO);
            String input = txtInput.getString();
            int temp;
            if(input.length()>0){
                temp = Integer.parseInt(input);
            } else{
                temp=0;
            }
            alert.setTimeout(3000);
            if(temp > rndNum){
                alert.setString("大了，笨蛋！");
                Display.getDisplay(this).setCurrent(alert);
            }
            if(temp == rndNum){
                alert.setString("佩服佩服！");
                Display.getDisplay(this).setCurrent(alert);
                //this.startApp();
            }
            if(temp < rndNum){
                alert.setString("小了，笨蛋！");
                Display.getDisplay(this).setCurrent(alert);
            }
            txtInput.setString("");
        }
    }
   
}