CODEWITHSUNDEEP
javanetwork-programmingmac-address
saplingPro
saplingPro

Reputation: 21329

Why do I get a blank MAC address?

The following program is meant to print the MAC address of my node. But it prints a blank. I checked it for null but it isn't null. Why would I get a blank MAC address ? What mistake am I committing ?

import java.net.InetAddress;
import java.net.NetworkInterface;

class Tester {
public static void main(String args[]) {
    try {
      InetAddress address = InetAddress.getByName("localhost");
      NetworkInterface ni = NetworkInterface.getByInetAddress(address);
      byte mac[] = ni.getHardwareAddress();
      if(mac == null) {
        System.out.println("Mac address is null");
      } else {
        System.out.println("Else block!");
        String macAdd = new String(mac);
        System.out.println(macAdd);
      }

    } catch(Exception exc) {
       exc.printStackTrace();
    }
}
}

Note: mac == null is false.

Upvotes: 1

Views: 2977

Answers (5)

Bhavik Ambani
Bhavik Ambani

Reputation: 6657

You should get localhost by InetAddress.getLocalHost(); instead of InetAddress.getByName("localhost");.Please refer my below example for the solution of your problem.

import java.net.InetAddress;
import java.net.NetworkInterface;

public class Tester {
    public static void main(String args[]) {
        try {
            InetAddress address = InetAddress.getLocalHost();
            NetworkInterface ni = NetworkInterface.getByInetAddress(address);
            byte mac[] = ni.getHardwareAddress();
            if (mac == null) {
                System.out.println("Mac address is null");
            } else {
                System.out.println("Else block!");
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < mac.length; i++) {
                    sb.append(String.format("%02X%s", mac[i], (i < mac.length - 1) ? "-" : ""));        
                }
                String macAdd = new String(sb);
                System.out.println(macAdd);
            }

        } catch (Exception exc) {
            exc.printStackTrace();
        }
    }
}

Output

Else block!
44-87-FC-F1-D4-77

NOTE :-

Remember that it is important to convert the mac address recieved into readable hexadecimal format, so I have written the below code block. If you dont do that then you will received garbage text as D‡üñÔw.

            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < mac.length; i++) {
                sb.append(String.format("%02X%s", mac[i], (i < mac.length - 1) ? "-" : ""));        
            }
            String macAdd = new String(sb);

Upvotes: 1

ChrisW
ChrisW

Reputation: 56123

The MAC address is an array of bytes, the first of which may be zero.

To print it you need to convert it to a printable, alphanumeric (e.g. hexadecimal) format, for example using String.format as shown in Bhavik Ambani's answer.

Upvotes: 0

Alexander Pavlov
Alexander Pavlov

Reputation: 32296

According to this discussion, "Well, the interface that reacts to "localhost" is usually the loopback device, which doesn't have a MAC address, so that might be your reason."

Upvotes: 4

Jesper Bangsholt
Jesper Bangsholt

Reputation: 534

If you check the JavaDocs for Java 7, you will notice there's the getLocalhost() which is what you probably want.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533740

I have never seen a localhost loop back interface with a MAC address. I suspect it's not very useful.

System.out.println(Arrays.toString(mac));

prints

[]

which is not surprising as its only a virtual software device.

Upvotes: 2

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