Why does java NetworkInterface.getHardwareAddress return empty byte array on Windows?

Question

I have the following code on a Windows machine:

for(Enumeration enm = NetworkInterface.getNetworkInterfaces(); enm.hasMoreElements();){
  NetworkInterface network = (NetworkInterface) enm.nextElement();
    if(null != network.getHardwareAddress()){
      return EthernetAddress.valueOf(network.getHardwareAddress());
    }
 }

This fails because the network.getHardwareAddress() returns an empty byte array, instead of null as stated in the javadocs for NetworkInterface. Does anyone know why this may happen?

Peter Lawrey · Accepted Answer · 2011-03-30 11:21:48Z

1

I did this and saw that the loopback (which apeared first) has no mac address.

My guess is that null is intended for when the OS returns that the MAC was unavailable. However it may have returned empty data instead.

On Linux, it doesn't show me the loopback.

edited Mar 30, 2011 at 11:21

answered Mar 30, 2011 at 11:16

Peter Lawrey

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1 Comment

Sam Ginrich May 16 at 8:59

loopback is not a physical adapter and the null-return complies the spec of getHardwareAddress()

Yogesh Seralia · Accepted Answer · 2015-08-11 10:15:43Z

-1

The byte array returned from network.getHardwareAddress() gets null if you are not connected to any network (LAN or WAN) hence it returns null value

edited Aug 11, 2015 at 10:15

answered Jun 9, 2015 at 12:39

Yogesh Seralia

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1 Comment

Sam Ginrich May 19 at 6:48

The hardware address is visible, when the adapter is active, no link required

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