java中的UDP套接字编程

Question

This sample code shown bellow:

public class UDPServer
{

    enter code here
    /**
     * @param args
     */
    public static void main(String[] args) throws Exception{
        // TODO Auto-generated method stub
        DatagramSocket serverSocket=new DatagramSocket(9876);
        byte[] receiveData=new byte[1024];
        byte[] sendData=new byte[1024];
        while(true)
        {
            DatagramPacket receivePacket=new DatagramPacket(receiveData, receiveData.length);
            String sentence=new String(receivePacket.getData());
            InetAddress IPAddress=receivePacket.getAddress();
            int port=receivePacket.getPort();
            String capitalizedSentennce=sentence.toUpperCase();
            sendData=capitalizedSentennce.getBytes();
            DatagramPacket sendPacket=new DatagramPacket(sendData, sendData.length,IPAddress,port);
            serverSocket.send(sendPacket);
        }
    }

}

is giving the following error when executed:

 Exception in thread "main" java.lang.IllegalArgumentException: Port out of range:-1
        at java.net.DatagramPacket.setPort(Unknown Source)
        at java.net.DatagramPacket.<init>(Unknown Source)
        at java.net.DatagramPacket.<init>(Unknown Source)
        at UDPServer.main(UDPServer.java:21)

Can someone help me to resolve it out? Also if possible please provide additional information why it happens.

Answer 1

You forgot to receive anything into the receivePacket. So there is nothing there. No port number, no source address, no data.