Question

I was having a problem to get the mac address of a machine, which was solved in this question using the follow code:

Process p = Runtime.getRuntime().exec("getmac /fo csv /nh"); 
java.io.BufferedReader in = new java.io.BufferedReader(new  java.io.InputStreamReader(p.getInputStream())); 
String line; 
line = in.readLine();         
String[] result = line.split(","); 

System.out.println(result[0].replace('"', ' ').trim()); 

However, I would like to know why this code is not working. Every time it reads the MAC address it returns a different value. First I thought it was because getHash, maybe using a timestamp I dont know… But even removing it the result changes.

Code

    public static byte[] getMacAddress() {
        try {
            Enumeration<NetworkInterface> nwInterface = NetworkInterface.getNetworkInterfaces();
            while (nwInterface.hasMoreElements()) {
                NetworkInterface nis = nwInterface.nextElement();
                if (nis != null) {
                    byte[] mac = nis.getHardwareAddress();
                    if (mac != null) {
                        /*
                         * Extract each array of mac address and generate a
                         * hashCode for it
                         */
                        return mac;//.hashCode();
                    } else {
                        Logger.getLogger(Utils.class.getName()).log(Level.WARNING, "Address doesn't exist or is not accessible");
                    }
                } else {
                    Logger.getLogger(Utils.class.getName()).log(Level.WARNING, "Network Interface for the specified address is not found.");
                }
                return null;
            }
        } catch (SocketException ex) {
            Logger.getLogger(Utils.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }
}

Output example (i’m printing directly from byte array, but its enough to see that different i think)

[B@91cee
[B@95c083
[B@99681b
[B@a61164
[B@af8358
[B@b61fd1
[B@bb7465
[B@bfc8e0
[B@c2ff5
[B@c8f6f8
[B@d251a3
[B@d6c16c
[B@e2dae9
[B@ef5502
[B@f7f540
[B@f99ff5
[B@fec107

Thanks in advance

Answer 1

B@91cee actually is the result toString() method of the byte[] arrays.

I would suggest you print the value using new String(mac) instead.

byte[].toString() is implemented as:

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

Since default Object.hashCode() is implemented as address in memory, thus it is not consistent as you are creating new Object each time.

Edit:

Since the returned byte is in hex, so you should convert it into decimal String. The code can see from here