Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();
while (networkInterfaces.hasMoreElements()) {
  NetworkInterface ni = networkInterfaces.nextElement();
 
  // up and running only
  if(!ni.isUp())
    continue;
  byte[] hardwareAddress = ni.getHardwareAddress();
  if (hardwareAddress != null) {
    String[] hexadecimalFormat = new String[hardwareAddress.length];
    for (int i = 0; i < hardwareAddress.length; i++)
      hexadecimalFormat[i] = String.format("%02X", hardwareAddress[i]);
    String mac = String.join("-", hexadecimalFormat);
    System.out.println(mac);
  }
}