Problem compiling sample multicast networking program

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Benjamin

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Sep 30, 2016, 11:16:14 AM9/30/16

to JPassion.com: Java Programming

Hello,

First I'd like to say I am really pleased with your course layout thus far. I seem to be having a problem compiling your sample multicast networking program on my mac.

The exception/compiler output is as follows:

run:

MulticastSocket is created at port 5000

Exception in thread "main" java.net.SocketException: Can't assign requested address

at java.net.PlainDatagramSocketImpl.join(Native Method)

at java.net.AbstractPlainDatagramSocketImpl.join(AbstractPlainDatagramSocketImpl.java:179)

at java.net.MulticastSocket.joinGroup(MulticastSocket.java:323)

at MulticastChatServer.main(MulticastChatServer.java:27)

/Users/Benjamin/Library/Caches/NetBeans/8.1/executor-snippets/run.xml:53: Java returned: 1

BUILD FAILED (total time: 0 seconds)

The code is:

import java.net.*;

public class MulticastChatServer {

public static void main(String args[])

throws Exception {

// Default port number we are going to use

int portnumber = 5000;

if (args.length >= 1) {

portnumber = Integer.parseInt(args[0]);

}

// Create a MulticastSocket

MulticastSocket serverMulticastSocket =

new MulticastSocket(portnumber);

System.out.println("MulticastSocket is created at port " + portnumber);

// Determine the IP address of a host, given the host name

// The host name can either be a machine name, such as "java.sun.com",

// or a textual representation of its IP address. If a literal IP

// address is supplied, only the validity of the address format is checked.

InetAddress group = InetAddress.getByName("225.4.5.6");

// getByName- returns IP address of given host

serverMulticastSocket.joinGroup(group);

System.out.println("joinGroup method is called...");

boolean infinite = true;

// Continually receives data and prints them

while (infinite) {

byte buf[] = new byte[1024];

DatagramPacket data =

new DatagramPacket(buf, buf.length);

serverMulticastSocket.receive(data);

String msg =

new String(data.getData()).trim();

System.out.println("Message received from client = " + msg);

}

serverMulticastSocket.close();

}

My network interface configuration is as follows:

Last login: Wed Sep 28 18:26:58 on ttys000

Benjamins-MacBook-Pro:~ Benjamin$ ifconfig

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384

options=3<RXCSUM,TXCSUM>

inet6 ::1 prefixlen 128

inet 127.0.0.1 netmask 0xff000000

inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1

nd6 options=1<PERFORMNUD>

gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280

stf0: flags=0<> mtu 1280

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500

ether a4:5e:60:d9:ad:21

inet6 fe80::a65e:60ff:fed9:ad21%en0 prefixlen 64 scopeid 0x4

inet 192.168.1.10 netmask 0xffffff00 broadcast 192.168.1.255

nd6 options=1<PERFORMNUD>

media: autoselect

status: active

en1: flags=963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX> mtu 1500

options=60<TSO4,TSO6>

ether 4a:00:01:1f:c8:30

media: autoselect <full-duplex>

status: inactive

en2: flags=963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX> mtu 1500

options=60<TSO4,TSO6>

ether 4a:00:01:1f:c8:31

media: autoselect <full-duplex>

status: inactive

p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304

ether 06:5e:60:d9:ad:21

media: autoselect

status: inactive

awdl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1484

ether de:39:ac:c0:e3:7c

inet6 fe80::dc39:acff:fec0:e37c%awdl0 prefixlen 64 scopeid 0x8

nd6 options=1<PERFORMNUD>

media: autoselect

status: active

bridge0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500

options=63<RXCSUM,TXCSUM,TSO4,TSO6>

ether a6:5e:60:9d:fb:00

Configuration:

id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0

maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200

root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0

ipfilter disabled flags 0x2

member: en1 flags=3<LEARNING,DISCOVER>

ifmaxaddr 0 port 5 priority 0 path cost 0

member: en2 flags=3<LEARNING,DISCOVER>

ifmaxaddr 0 port 6 priority 0 path cost 0

nd6 options=1<PERFORMNUD>

media: <unknown type>

status: inactive

utun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500

inet6 fe80::935a:dea6:fc62:3b81%utun0 prefixlen 64 scopeid 0xa

nd6 options=1<PERFORMNUD>

Benjamins-MacBook-Pro:~ Benjamin$ -Djava.net.preferIPv4Stack=true

-bash: -Djava.net.preferIPv4Stack=true: command not found

Benjamins-MacBook-Pro:~ Benjamin$

My basic computer info is in attachment:

Sang Shin

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Sep 30, 2016, 12:00:16 PM9/30/16

to benjam...@gmail.com, JPassion.com: Java Programming

On 9/30/2016 6:59 AM, Benjamin wrote:

Hello,

First I'd like to say I am really pleased with your course layout thus far. I seem to be having a problem compiling your sample multicast networking program on my mac.

Thanks for the kind words. I just tried MulticastServer and it compiled
and run fine.

The message below indicates that the compilation worked fine but
when you run it, the port 5000 cannot be assigned, which means
someone already uses the port.

Try "netstat -a |grep 5000" and see if port 5000 is already taken before you
run the app and kill the process that uses it.

-Sang

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