class demo updates

examples/src/UdpMulticastExamples/UdpReceiver.java

@@ -11,12 +11,13 @@ import java.net.*;
  * Start this before launching UdpSender.
  * 
  * @see https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html
+ * @see https://en.wikipedia.org/wiki/User_Datagram_Protocol
  * @author mcgredo
  * @author brutzman
  */
 public class UdpReceiver 
 {
-    public static final int       SENDING_PORT = 1414;
+//  public static final int       SENDING_PORT = 1414; // port used by UdpSender, unneeded here
     public static final int     RECEIVING_PORT = 1415;
     public static final String DESINATION_HOST = "localhost";
 
@@ -57,22 +58,23 @@ public class UdpReceiver
                 udpSocket.receive(receivePacket); // blocks until packet is received
                 
                 // values of interest follow. order and types of what was sent must match what you are reading!
-                firstInt     = dis.readInt();
+                firstInt     = dis.readInt();     // packetID
                 secondFloat  = dis.readFloat();
-                thirdString  = dis.readUTF();
-                isEvenParity = dis.readBoolean();
-                dis.reset(); // clear the input stream after reading
+                thirdString  = dis.readUTF();     // string value with guaranteed encoding, matches UTF-8 is 8 bit
+                isEvenParity = dis.readBoolean(); // ok, we've gotten everything we're looking for.  
                 
-                if  (isEvenParity)
+                dis.reset(); // now clear the input stream after reading, in preparation for next loop
+                
+                if  (isEvenParity) 
                      padding = " ";
                 else padding = "";
                 
-                System.out.println(UdpReceiver.class.getName() + 
-                                      ", first int value="    + firstInt + 
-                                   ", second float value="    + secondFloat + 
-                                   ", third String value=\""  + thirdString + "\"" + // note that /" is literal quote character
-                                          " parity value="    + isEvenParity + padding +
-                                   ", packet counter="        + packetCount);
+                System.out.println("[" + UdpReceiver.class.getName() + "]" + 
+                                               " 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 +
+                                     " packet counter="        + packetCount);
             }
         }
         catch(IOException e)
@@ -80,10 +82,11 @@ public class UdpReceiver
             System.err.println("Problem with UdpReceiver, see exception trace:");
             System.err.println(e);
         } 
-        finally // clean up prior to exit, don't want to leave behind zombie
+        finally // clean up prior to exit, don't want to leave behind zombie socket
         {
             if (udpSocket != null)
                 udpSocket.close();
+            System.out.println(UdpReceiver.class.getName() + " complete."); // all done
         }
     }
 }

examples/src/UdpMulticastExamples/UdpSender.java

@@ -12,22 +12,24 @@ import java.net.*;
  * Start this before launching UdpReceiver.
  * 
  * @see https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html
+ * @see https://en.wikipedia.org/wiki/User_Datagram_Protocol
  * @author mcgredo
  * @author brutzman
  */
 public class UdpSender 
 {
     // System properties: https://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html
-    public static final String          MY_NAME = System.getProperty("user.name"); // guru incantation   8)
-    public static final int        SENDING_PORT = 1414;
-    public static final int      RECEIVING_PORT = 1415;
-    public static final String DESTINATION_HOST = "localhost"; // localhost 127.0.0.1 or argon 10.1.105.1
+    public static final String            MY_NAME = System.getProperty("user.name"); // guru incantation   8)
+    public static final int          SENDING_PORT = 1414;
+    public static final int        RECEIVING_PORT = 1415;
+    public static final int TOTAL_PACKETS_TO_SEND = 100;
+    public static final String   DESTINATION_HOST = "localhost"; // localhost 127.0.0.1 or argon 10.1.105.1
     
     @SuppressWarnings("SleepWhileInLoop")
     public static void main(String[] args) throws IOException 
     {
         DatagramSocket udpSocket = null;
-        DataOutputStream dos = null;
+        DataOutputStream  dos = null;
         int   packetID = 0;     // counter variable to send in packet
         float    value = -1.0f; // unreachable value is good sentinel to ensure expected changes occur
         String message = "Hello MV3500"; // no really
@@ -64,34 +66,33 @@ public class UdpSender
             // How do you know on the receiving side that you haven't received a
             // duplicate UDP packet, out-of-order packet, or dropped packet? your responsibility.
             
-            for (int index = 1; index <= 100; index++) // avoid infinite send loops in code, they can be hard to kill!
+            for (int index = 1; index <= TOTAL_PACKETS_TO_SEND; index++) // avoid infinite send loops in code, they can be hard to kill!
             {
                 packetID++;             // increment counter, prefer using explicit value to index
                 value = 100 - packetID; // countdown
-                boolean isEvenParity = ((packetID % 2) == 0); // % is modulo operator
+                boolean isPacketIdEvenParity = ((packetID % 2) == 0); // % is modulo operator; result 0 is even parity, 1 is odd parity
                 
                 // values of interest follow. order and types of what was sent must match what you are reading!
                 dos.writeInt    (packetID);
                 dos.writeFloat  (value);
-                dos.writeUTF    (message);
-                dos.writeBoolean(isEvenParity);
+                dos.writeUTF    (message); // string value with guaranteed encoding, matches UTF-8 is 8 bit
+                dos.writeBoolean(isPacketIdEvenParity);
+                
                 dos.flush(); // sends DataOutputStream to ByteArrayOutputStream
                 byteArray = baos.toByteArray();    // OK so go get the flushed result...
                 datagramPacket.setData(byteArray); // and put it in the packet...
                 udpSocket.send(datagramPacket);    // and send it away. boom gone, nonblocking.
                 
-                if  (isEvenParity)
+                if  (isPacketIdEvenParity)
                      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 + "\", " + isEvenParity +
-                                   ")" + padding + " as packet #" + index + " of 100");
+                System.out.println("[" + UdpSender.class.getName() + "] " + MY_NAME + " " + sourceAddress + 
+                                   " sent values(" + packetID + "," + value + ",\"" + message + "\"," + isPacketIdEvenParity +
+                                   ")" + padding + " as packet #" + index + " of " + TOTAL_PACKETS_TO_SEND);
                 baos.reset(); // clear the output stream after sending
             }
-            System.out.println(UdpSender.class.getName() + " complete."); // all done
-
         }
         catch (IOException | InterruptedException e)
         {
@@ -105,6 +106,7 @@ public class UdpSender
             
             if (dos != null)
                 dos.close();
+            System.out.println(UdpSender.class.getName() + " complete."); // all done
         }
     }
 }