nullpointerexception - java null pointer exception- Occurs at varying points in while loop -

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i have following java while loop:

while(true){     byte buffer[] = new byte[max_pdu_size];     packet = new datagrampacket(buffer, buffer.length);      socket.receive(packet);      pdu pdu = pdufactory.createpdu(packet.getdata());      system.out.print("got pdu of type: " + pdu.getclass().getname());     if(pdu instanceof entitystatepdu){         entityid eid = ((entitystatepdu)pdu).getentityid();         vector3double position = ((entitystatepdu)pdu).getentitylocation();         system.out.print(" eid:[" + eid.getsite() + ", " + eid.getapplication() + ", " + eid.getentity() + "] ");         system.out.print(" location in dis coordinates: [" + position.getx() + ", " + position.gety() + ", " + position.getz() + "]");         }     system.out.println();     } }

the intended function of while loop capture pdus being sent across network, , display information them.

when run code, go output had intended in console- @ least initially... after has returned information number of pdus, got error displayed in console (can't remember said now- thought may because trying capture pdu when there wasn't 1 being sent).

i have tried amending code account occasion pdu may not being received on network @ time trying capture information pdu surrounding code following try- catch loop:

try{     socket = new multicastsocket(espdusender.port);     address = inetaddress.getbyname(espdusender.default_multicast_group);     socket.joingroup(address);      while(true){         byte buffer[] = new byte[max_pdu_size];         packet = new datagrampacket(buffer, buffer.length);          socket.receive(packet);          pdu pdu = pdufactory.createpdu(packet.getdata());          system.out.print("got pdu of type: " + pdu.getclass().getname());         if(pdu instanceof entitystatepdu){             entityid eid = ((entitystatepdu)pdu).getentityid();             vector3double position = ((entitystatepdu)pdu).getentitylocation();             system.out.print(" eid:[" + eid.getsite() + ", " + eid.getapplication() + ", " + eid.getentity() + "] ");             system.out.print(" location in dis coordinates: [" + position.getx() + ", " + position.gety() + ", " + position.getz() + "]");             }         system.out.println();         }     } catch(exception e){     system.out.println(e);     system.out.println("this error being generated"); }

however, when run code- still displays first x number of dis packets captures (x varies every time run code), gives me java.lang.nullpointerexception. understand, occur either because pdu code has captured not contain information, (i.e. 'empty' pdu), or because attempting receive pdu when there isn't 1 being sent on network.

how can make code 'skip' occasion doesn't receive pdu, , keep running? or there else should rid of error?

this may not fix problem (won't know until put stack trace up), check see if pdu null before using it.

while(true){     byte buffer[] = new byte[max_pdu_size];     packet = new datagrampacket(buffer, buffer.length);      socket.receive(packet);      pdu pdu = pdufactory.createpdu(packet.getdata());      if (pdu != null) {         system.out.print("got pdu of type: " + pdu.getclass().getname());         if(pdu instanceof entitystatepdu){             entityid eid = ((entitystatepdu)pdu).getentityid();             vector3double position = ((entitystatepdu)pdu).getentitylocation();             system.out.print(" eid:[" + eid.getsite() + ", " + eid.getapplication() + ", " + eid.getentity() + "] ");             system.out.print(" location in dis coordinates: [" + position.getx() + ", " + position.gety() + ", " + position.getz() + "]");             }         system.out.println();     } }

if stack trace out, can change actual problem.


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