? ???? PC?? ????? UDP ??????? ???? ??? ?????.
?? PC??? ?? ??? ??? ?????. ?? ?????.

private final ScheduledExecutorService askService= Executors.newSingleThreadScheduledExecutor();

public void runWaitConnectThead(){
        askService.scheduleAtFixedRate(this::sendAskMessage, 0, boardCastConfig.getWAIT_MS(), TimeUnit.MILLISECONDS);
    }
protected void sendAskMessage(){
        byte[] message = this.hostName.getBytes();
        try (DatagramSocket datagramSocket = new DatagramSocket()) {
            datagramSocket.setBroadcast(true);
            InetAddress boardcastAddr = InetAddress.getByName("255.255.255.255");
            DatagramPacket datagramPacket = new DatagramPacket(message, message.length, boardcastAddr, 1885);
            datagramSocket.send(datagramPacket);
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }

?? ? ?? ?? ???? AskService? ?? ????(? ?? ????) ????? UDP ??? ??????? "sendAskMessage()" ??? ?? ?????. ? ????? 5??? ?????.

?? 50%? ??? ??????.
?? ??? ???? ?? AndroidMnifest.xml ??? ?? ??? ???? ???. ??? ??? ??????? ??? ? ????.
??? ??? ????.

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />

?? ?? MainActivity?? ???? ??? ??? ?? ??? ??? ?????. ??? AndroidManifest.xml ??? ? ???? ???? ?? ?? ???.

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Intent waitBoardCastService=new Intent(this, WaitBoardCastService.class);
        startService(waitBoardCastService);
    }
}

<service android:name=".on_wait.WaitBoardCastService"/>

?? ?? ??? ??? ? ????. ? ???? ???? ????.
①? ??? ??(? ???? ???? ???? ?? ?????. ?? ????? ???? ??? ???? ??????? ??? ? ????)
②????? ?? ??(? ??? ?? ????, ??? ??? UDP ??? ?? ? ????)
③UDP ?? ??

WifiManager wifi =(WifiManager)getSystemService(MyApplication.WIFI_SERVICE);
WifiManager.MulticastLock lock = wifi.createMulticastLock("any_tag");
lock.acquire();
try {
    DatagramSocket socket = new DatagramSocket(1885);
    byte[] receiveData = new byte[1024];
    DatagramPacket receivePacket = new DatagramPacket(receiveData, 
    receiveData.length);
    Log.v("hello","waiting");
    socket.receive(receivePacket);
    String receiveMessage = new String(receivePacket.getData(), 0,receivePacket.getLength());
    Log.v("hello","received!");
    socket.close();
} catch (IOException e) {
    Toast.makeText(MyApplication.getContext(), "NetWork Error",Toast.LENGTH_LONG).show();
} finally {
    lock.release();
}

? ??:

? ??? Android? PC?? UDP ?????? ??? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!