Why receiveData in UDP Socket contains "square" char? - sockets

Question

When i run Server and Client, type a string form Client to Server, Server response that string and "square" char.
I have consulted many codes but the result is still the same........................................................................................................................................................................................................................................................................................................
My Server :
public class serverUDP {
public static void main(String args[]) throws Exception {
DatagramSocket serverSocket = new DatagramSocket(9876);
while(true) {
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[2048];
// receive packet
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
String sentence = new String(receivePacket.getData());
InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();
String sentence_to_client = sentence+ " (server accpeted!)";
// send packet
sendData = sentence_to_client.getBytes();
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);
serverSocket.send(sendPacket);
}
}
}
My Client :
public class clientUDP {
public static void main(String args[]) throws Exception {
DatagramSocket clientSocket = new DatagramSocket(6789);
InetAddress IPAddress = InetAddress.getByName("localhost");
while(true){
byte[] sendData = new byte[1024];
byte[] receiveData = new byte[2048];
// input
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
String sentence = inFromUser.readLine();
// send packet
sendData = sentence.getBytes();
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
clientSocket.send(sendPacket);
// receive packet
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
clientSocket.receive(receivePacket);
String modified_Sentence = new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modified_Sentence);
if(sentence.compareTo("quit") == 0)
break;
}
clientSocket.close();
}
}
Result: String + "square" char