sockets - Java UDP Connection -

i'm using netbeans ide trying make udp connection between client , server, it's simple program udpclient send string udpserver , server capitalize string , sends client.i made client side , server side in separated projects.

my class code client udpclient :

    package udpclient;       import java.io.*;     import java.net.*;      public class udpclient {          public static void main(string[] args) throws ioexception{              //get input user             bufferedreader user_in = new bufferedreader(                     new inputstreamreader(system.in));              //create udp socket connection             datagramsocket socket = new datagramsocket();              //creat buffers process data             byte[] indata = new byte[1024];             byte[] outdata = new byte[1024];              //get ip destination wanted             inetaddress ip = inetaddress.getbyname("localhost");              //read data user             system.out.println("enter data send server: ");             outdata = user_in.readline().getbytes();               /*              * make pkts interaction              */             //send pkts             datagrampacket sendpkt = new datagrampacket(outdata, outdata.length, ip, 9876);             socket.send(sendpkt);              //receive pkts             datagrampacket recievepkt = new datagrampacket(indata, indata.length);             socket.receive(recievepkt);              system.out.println("replay server: "+recievepkt.getdata());          }     } 

and server side class udpserver:

    package udpserver;      import java.io.*;     import java.net.*;      public class udpserver {           public static void main(string[] args) throws ioexception{             // todo code application logic              //connection             datagramsocket socket = new datagramsocket();              //pkt buffers             byte[] inserver = new byte[1024];             byte[] outserver = new byte[1024];              //receive pkt             datagrampacket rcvpkt = new datagrampacket(inserver,inserver.length);             socket.receive(rcvpkt);             //display receive             system.out.println("packet received!");               //retrive pkt info send response same sender             inetaddress ip = rcvpkt.getaddress();             int port = rcvpkt.getport();              //process data             string temp = new string(rcvpkt.getdata());             temp = temp.touppercase();             outserver = temp.getbytes();              //send response packet sender             datagrampacket sndpkt = new datagrampacket(outserver, outserver.length, ip, port);             socket.send(sndpkt);          }     } 

make in count program runs , outputs no error. server doesn't receive packet @ , didn't interact client. why happened ?

you haven't specified listening port in server server listen on random available port.

try on server side

datagramsocket socket = new datagramsocket(9876);