updated example program, works fine

examples/src/UdpMulticastExamples/UdpReceiver.java

@@ -20,16 +20,15 @@ public class UdpReceiver
 {
 //  public static final int        SENDING_PORT = 1414;        // port used by UdpSender, unneeded here
     /** socket value of shared interest */
-    public static final int      RECEIVING_PORT = 1415;        // sharable
+    public static final int      UDP_PORT = 1415;        // sharable
     /** socket value of shared interest */
     public static final String DESTINATION_HOST = "localhost";
 
     /**
      * Program invocation, execution starts here
      * @param args command-line arguments
-     * @throws java.io.IOException execution error
      */
-    public static void main(String[] args) throws IOException
+    public static void main(String[] args)
     {
         DatagramSocket udpSocket = null;
         
@@ -38,7 +37,7 @@ public class UdpReceiver
             System.out.println(UdpReceiver.class.getName() + " started...");
             
             // Create a UDP socket
-            udpSocket = new DatagramSocket(RECEIVING_PORT);
+            udpSocket = new DatagramSocket(UDP_PORT);
             udpSocket.setReceiveBufferSize(1500); // how many bytes are in buffer?  MTU=1500 is good
             udpSocket.setBroadcast(false);        // we're just receiving here
 //            udpSocket.setReuseAddress(true);
@@ -62,8 +61,13 @@ public class UdpReceiver
                 packetCount++; // good practice to increment counter at start of loop, when possible
                 udpSocket.receive(receivePacket); // blocks until packet is received
                 
-                System.out.println("UdpReceiver address/port: " + udpSocket.getInetAddress().getHostAddress() + "/" + RECEIVING_PORT);
-                
+                if (packetCount == 1)
+                {                
+                    if  (udpSocket.getInetAddress() == null)
+                         System.out.println("UdpReceiver address/port: UDP socket address null (loopback)" + "/" + UDP_PORT);
+                    else System.out.println("UdpReceiver address/port: " + udpSocket.getInetAddress().getHostAddress() + "/" + UDP_PORT);
+                }
+
                 // values of interest follow. order and types of what was sent must match what you are reading!
                 firstInt     = dis.readInt();     // packetID
                 secondFloat  = dis.readFloat();
@@ -77,7 +81,8 @@ public class UdpReceiver
                 else padding = "";
                 
                 System.out.println("[" + UdpReceiver.class.getName() + "]" + 
-                                               " packetID="   + firstInt +            // have output message use same name as sender
+                                                    " port="   + UDP_PORT +
+                                                " packetID="   + firstInt +            // have output message use same name as sender
                                      ", second float value="   + secondFloat  + 
                                      ", third String value=\"" + thirdString  + "\"" + // note that /" is literal quote character
                                     " isPacketIdEvenParity="   + isEvenParity + ","  + padding +

examples/src/UdpMulticastExamples/UdpSender.java

@@ -22,7 +22,7 @@ public class UdpSender
     private static final String            MY_NAME = System.getProperty("user.name"); // guru incantation   8)
 //  public  static final int          SENDING_PORT = 1414; // not needed, can let system choose an open local port
     /** socket value of shared interest */
-    public  static final int        RECEIVING_PORT = UdpReceiver.RECEIVING_PORT; // 1415; ensure consistent
+    public  static final int              UDP_PORT = UdpReceiver.UDP_PORT; // 1415; ensure consistent
     private static final int TOTAL_PACKETS_TO_SEND = 100;
     
     /** socket value of shared interest */
@@ -33,10 +33,9 @@ public class UdpSender
     /**
      * Program invocation, execution starts here
      * @param args command-line arguments
-     * @throws java.io.IOException execution error
      */
     @SuppressWarnings("SleepWhileInLoop")
-    public static void main(String[] args) throws IOException 
+    public static void main(String[] args)
     {
         DatagramSocket udpSocket = null;
         DataOutputStream  dos = null;
@@ -69,9 +68,9 @@ public class UdpSender
             // ID of the host we are sending from
             InetAddress      sourceAddress = InetAddress.getByName("localhost"); // possibly identical if source not modified
             
-            DatagramPacket datagramPacket = new DatagramPacket(byteArray, byteArray.length, destinationAddress, RECEIVING_PORT);
+            DatagramPacket datagramPacket = new DatagramPacket(byteArray, byteArray.length, destinationAddress, UDP_PORT);
             
-            System.out.println("UdpSender address/port: " + destinationAddress.getHostAddress() + "/" + RECEIVING_PORT);
+            System.out.println("UdpSender address/port: " + destinationAddress.getHostAddress() + "/" + UDP_PORT);
        
             // Hmmm, how fast does UDP stream go? Does UDP effectively slow packets down, or does
             // this cause network problems? (hint: yes for an unlimited send rate, unlike TCP).
@@ -100,9 +99,10 @@ public class UdpSender
                      padding = " ";
                 else padding = "";
             
-                Thread.sleep(1000); // Send packets at rate of one per second
-                System.out.println("[" + UdpSender.class.getName() + "] " + MY_NAME + " " + sourceAddress + 
-                                   " sent values(" + packetID + "," + value + ",\"" + message + "\"," + isPacketIdEvenParity +
+                Thread.sleep(100); // Send packets at rate of one per second
+                System.out.println("[" + UdpSender.class.getName() + "] " + MY_NAME + " " + sourceAddress +
+                                   " port=" + UDP_PORT +
+                                   " has sent values (" + packetID + "," + value + ",\"" + message + "\"," + isPacketIdEvenParity +
                                    ")" + padding + " as packet #" + index + " of " + TOTAL_PACKETS_TO_SEND);
                 baos.reset(); // clear the output stream after sending
             }   // end for loop
@@ -116,9 +116,16 @@ public class UdpSender
         {
             if (udpSocket != null)
                 udpSocket.close();
-            
-            if (dos != null)
-                dos.close();
+            try
+            {
+                if (dos != null)
+                    dos.close();
+            }
+            catch (IOException e)
+            {
+                System.err.println("Problem with UdpSender, see exception trace:");
+                System.err.println(e);
+            } 
             System.out.println(UdpSender.class.getName() + " complete."); // all done
         }
     }