The <code>NetworkInterface</code> class has no public constructor. Therefore,
you cannot just create a new instance of this class with the <code>new</code>
operator. Instead, the following static methods are 
available so that you can retrieve the interface details from the system:
<code>getByInetAddress()</code>, <code>getByName()</code>, and 
<code>getNetworkInterfaces()</code>. The first two methods are
used when you already know the IP address or the name of the 
particular interface. The third method, <code>getNetworkInterfaces()</code>
returns the complete list of interfaces on the machine.
<p>
Network interfaces can be hierarchically organized.
The <code>NetworkInterface</code> class includes two methods,
<code>getParent()</code> and <code>getSubInterfaces()</code>, that are 
pertinent to
a network interface hierarchy. The <code>getParent()</code> method returns
the parent <code>NetworkInterface</code> of an interface. If a network 
interface is a subinterface, <code>getParent()</code> returns a non-null
value. The <code>getSubInterfaces()</code> method returns all the
subinterfaces of a network interface.
<p>
The following example program lists the name of all the network interfaces and
subinterfaces (if any exist) on a machine.

import java.io.*;
import java.net.*;
import java.util.*;
import static java.lang.System.out;

public class ListNIFs 
{
    public static void main(String args[]) throws SocketException {
        Enumeration&lt;NetworkInterface&gt; nets = NetworkInterface.getNetworkInterfaces();
        
        for (NetworkInterface netIf : Collections.list(nets)) {
            out.printf(&quot;Display name: %s\n&quot;, netIf.getDisplayName());
            out.printf(&quot;Name: %s\n&quot;, netIf.getName());
            displaySubInterfaces(netIf);
            out.printf(&quot;\n&quot;);
        }
    }

    static void displaySubInterfaces(NetworkInterface netIf) throws SocketException {
        Enumeration&lt;NetworkInterface&gt; subIfs = netIf.getSubInterfaces();
        
        for (NetworkInterface subIf : Collections.list(subIfs)) {
            out.printf(&quot;\tSub Interface Display name: %s\n&quot;, subIf.getDisplayName());
            out.printf(&quot;\tSub Interface Name: %s\n&quot;, subIf.getName());
        }
     }
}  
The following is sample output from the example program:

Display name: bge0
Name: bge0
    Sub Interface Display name: bge0:3
    Sub Interface Name: bge0:3
    Sub Interface Display name: bge0:2
    Sub Interface Name: bge0:2
    Sub Interface Display name: bge0:1
    Sub Interface Name: bge0:1

Display name: lo0
Name: lo0