android中activity的单例启动

 public static void startActivity(Context context, String className, long time) {        Intent intent = new Intent(Intent.ACTION_VIEW);        intent.setClassName(context, className);        intent.putExtra(EVENT_BEGIN_TIME, time);        intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT | Intent.FLAG_ACTIVITY_SINGLE_TOP);        context.startActivity(intent);    }