NetIf.java

import java.net.NetworkInterface;
import java.util.Enumeration;

public class NetIf {
  public static void main(String [] args) {
    try {
      Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces();
      while (en.hasMoreElements()) {
        NetworkInterface nif = en.nextElement();
        Enumeration<NetworkInterface> suben = nif.getSubInterfaces();
        while (suben.hasMoreElements()) {
          System.out.println(suben.nextElement().getName());
        }
        System.out.println(nif.getName());
      }
    } catch(Exception e) {
      e.printStackTrace();
    }
  }
}

output.sh

$ ifconfig -u
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
  # loopback device no status req'd 
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	status: active
p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304
	status: inactive
en3: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	status: inactive

$ java NetIf
en0
lo0