//关闭Activity的类
public class CloseActivityClass{ 
 
  public static List<Activity> activityList = new ArrayList<Activity>();
 
  public static void exitClient(Context ctx)
  {
   // 关闭所有Activity
   for (int i = 0; i < activityList.size(); i++)
   {
     if (null != activityList.get(i))
     {
       activityList.get(i).finish();
     }
   }
   ActivityManager activityMgr = (ActivityManager) ctx.getSystemService(Context.ACTIVITY_SERVICE );
   activityMgr.restartPackage(ctx.getPackageName());
   System.exit(0);
  }
}

CloseActivityClass.activityList.add(this);

CloseActivityClass.exitClient(MainActivity.this);