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);}}