Question

i have a weird problem. I am trying to write simple Client – Server app with chat option, but i ran into a problem – Object Input Stream reads wrong class. Error is:

Exception in thread "Thread-4" java.lang.ClassCastException: org.oxomoco.packets.PacketAlive cannot be cast to org.oxomoco.packets.PacketMessage
at org.oxomoco.server.SocketConnectionServer.run(SocketConnectionServer.java:52)
at java.lang.Thread.run(Unknown Source)

And it happens here:

 PacketMessage pm = (PacketMessage)ois.readObject();

Which is in loop that looks like this:

            while(true){




            //if(ois.readObject() instanceof PacketMessage){


            //  pm = (PacketMessage)ois.readObject();
            //  se.println(ois.readObject().toString());
            //}



            if((ois.readObject() instanceof PacketMessage)==true){
                System.out.println("It is: " + (ois.readObject() instanceof PacketMessage));

                PacketMessage pm = (PacketMessage)ois.readObject();

                se.acprintln(">>",uname + ": " +pm.getMsg());

            }
            if((ois.readObject() instanceof PacketAlive)==true){
                System.out.println("-it is: " + (ois.readObject() instanceof PacketAlive));
                PacketAlive pa = (PacketAlive)ois.readObject();
            }

    }

Somehow – even though i check instances – Object input stream is instance of PacketMessage when it should be instance of PacketAlive. Does anyone have an idea why, and of course – how to fix it?

Answer 1

You’re executing

ois.readObject()

several times, and getting a different object (of a different class?) each time. readObject() pulls each object from the stream, rather than leave it there.

Instead, read it, assign to a variable and then perform your tests etc. e.g.

while (true) {
   Object obj = ois.readObject();
   // do something with obj...