MultiThreaded Udp socket programming - multithreading

Question

This is the code for my client and server.
class Client1
{
Client1(int no)
{
try
{
String message;
message="Hello this is client "+no;
byte[] b =message.getBytes();
DatagramPacket dp = new DatagramPacket(b, b.length,InetAddress.getLocalHost(),3700);
DatagramSocket sender = new DatagramSocket();
sender.send(dp);
}catch (Exception e)
{
System.out.println("client shutdown");
}
}
}
Then my server class is
class Server1
{
int cnt=0;
String s1;
Server1()
{
try {
byte[] buffer = new byte[65536];
DatagramPacket incoming = new DatagramPacket(buffer, buffer.length);
DatagramSocket ds = new DatagramSocket(3700);
ds.receive(incoming);
byte[] data = incoming.getData();
String s = new String(data, 0, incoming.getLength());
System.out.println("Port" + incoming.getPort() + " on " + incoming.getAddress() + " sent this message:");
System.out.println(s.toUpperCase());
}
catch (IOException e)
{
System.err.println(e);
}
}
}
Then my runnable implementation is
class prothread implements Runnable {
//long time=0;
//int portno;
int flag=0; // this is to differentiate between a server and client
private String capitalizedSentence;
prothread(long l)
{
if(l==1)
{ // it is a server
flag=1;
}
else
{
flag=(int) l;
}
}
#Override
public void run(){
// TODO Auto-generated method stub
System.out.println("Starting thread");
if(flag==1)// Code for server
{
Server1 s=new Server1();
}
else // code for client
{
Client1 c=new Client1(flag);
}
}
}
Finally the class which deploys this client and server is
public class Samplepro31 {
public static void main(String[] args) {
// First i'm going to create a server and then clients for it
int i=1;
int cnt=0;
prothread[] p;
Thread[] th;
Random r =new Random();
// Array has been declared
p=new prothread[10];// Memory allocated to it
th= new Thread[1000];
p[0]=new prothread(1);
cnt=1;
//p[0].setportno(cnt);
th[0]=new Thread(p[0]);
th[0].start();
while(cnt<3)
{
p[cnt]=new prothread(cnt);
// here send the port number
th[cnt]=new Thread(p[cnt]);
//p[cnt1].setportno(cnt1);
th[cnt].start();
cnt++;
}
}
}
So problem I'm having is one server and only one client is running at a time
instead 2 clients should be running the o/p i'm getting is :
Starting thread
Starting thread
Starting thread
Inside clinet's constructor 2
java.net.BindException: Address already in use: Cannot bind
HELLO THIS IS CLIENT 2
So can anybody tell me what I'm doing wrong?

Answer 1

Don't bind the client to any particular port. Let the implementation select an available port to bind to.