android系统退出代码实现

android系统退出实现，代码如下：

package com.sms.util;

import java.util.LinkedList;
import java.util.List;

import android.app.Activity;
import android.app.Application;

//实现Activity退出
public class MyApplication extends Application{
    private List<Activity> activityList = new LinkedList<Activity>();
    private static MyApplication instance;
    
    private MyApplication(){
        
    }
    
    //单例实现返回MyApplication实例
    public static MyApplication getInstance(){
        if(null == instance){
            instance = new MyApplication();
        }
        return instance;
    }
    
    //Activity加入到List中
    public void addActivity(Activity activity){
        activityList.add(activity);
    }
    
    //遍历每个Activity退出
    public void exit(){
        for(Activity activity:activityList){
            activity.finish();
        }
        System.exit(0);
    }
}