android.os.Process.killProcess(android.os.Process.myPid())

System.exit(0);

ActivityManager manager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);  
manager.restartPackage(getPackageName());
<uses-permission android:name="android.permission.RESTART_PACKAGES" />

AndroidMainfest -->name -->app //声明该类为整个应用程序全局的实例

App.class:
ArrayList<Activity> activities;

public void onCreate(Bundle savedInstanceState) {
    App app = (App) getApplication();//获取应用程序全局的实例引用
    app.activities.add(this);  //把当前Activity放入集合中
}

public void onDestory(){
    App app = (App) getApplication();//获取应用程序全局的实例引用
    app.activities.remove(this); //把当前Activity从集合中移除
}

App app = (App) getApplication();
List<Activity> activities = app.activities;
for(Activity act:activities){
 act.finish();//显式结束
}