android已经到了一定的时间，如何调用服务来通知？

// 创建服务
public class MyNotificationService extends Service {
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // 创建通知
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this)
                .setSmallIcon(R.drawable.notification_icon)
                .setContentTitle("通知标题")
                .setContentText("通知内容");

        // 发送通知
        NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(1, builder.build());

        return super.onStartCommand(intent, flags, startId);
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

// 启动服务
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 启动服务
        Intent serviceIntent = new Intent(this, MyNotificationService.class);
        startService(serviceIntent);
    }
}