• Network Interface:
  • A connection between a computer and a (data communications) network
• Hardware Network Interfaces:
  • A network interface card (NIC) provides one or more network interfaces
• Software Network Interfaces:
  • Software can provide a network interface (e.g., the local loopback interface is implemented in software)

• Purpose:
  • An object that provides access to both hardware and software network interfaces
• Constructing NetworkInterface Objects:
  • The static NetworkInterface.getNetworkInterfaces() method
  • The getSubinterface() and getParent() retrieve subinterfaces (a.k.a., virtual interfaces) and parent interfaces respectively

javaexamples/internet/DisplayNIFs.java

import java.io.*;
import java.net.*;
import java.util.*;

/**
 * An application that displays all of the network interfaces
 * on this computer.
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class DisplayNIFs
{
    /**
     * The entry point of the application.
     *
     * @param args Command line arguments (-r for a recursive display)
     */
    public static void main(String[] args)
    {
        Enumeration<NetworkInterface> nifs;
        String indent;
        

        indent = "";
        if ((args != null) && (args.length > 0) && args[0].equals("-r")) 
            indent = " ";

        try
        {
            display(NetworkInterface.getNetworkInterfaces(), indent);
        }
        catch (SocketException se)
        {
            System.out.println("Unable to get network interfaces!");
        }
    }

    /**
     * Display the names of an Enumeration of NetworkInterface objects.
     *
     * @param nifs   The Enumeration
     * @param indent The indentation String ("" for none and no recursion)
     */
    private static void display(Enumeration<NetworkInterface> nifs, 
                                String indent) throws SocketException
    {
        while (nifs.hasMoreElements())
        {
            NetworkInterface nif = nifs.nextElement();
            
            System.out.printf("%s%s (%s)\n", indent,
                              nif.getDisplayName(), nif.getName());

            if (!indent.equals("")) display(nif.getSubInterfaces(), 
                                            indent+"\t");
            System.out.println();
        }
    }
}
        

• Getting the IP Address:
  • getInetAddresses() returns an Enumeration of InetAddress objects
• Getting the (Slightly More General) Interface Address:
  • getInterfaceAddresses() returns a List of InterfaceAddress objects

javaexamples/internet/DisplayAddresses.java

import java.io.*;
import java.net.*;
import java.util.*;

/**
 * An application that displays all of the network addresses
 * on this computer.
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class DisplayAddresses
{
    /**
     * The entry point of the application.
     *
     * @param args Command line arguments (ignored)
     */
    public static void main(String[] args)
    {
        Enumeration<NetworkInterface> nifs;

        try
        {
            display(NetworkInterface.getNetworkInterfaces());
        }
        catch (SocketException se)
        {
            System.out.println("Unable to get network interfaces!");
        }
    }

    /**
     * Display the addresses of an Enumeration of NetworkInterface objects.
     *
     * @param nifs   The Enumeration
     * @param indent The indentation String ("" for none and no recursion)
     */
    private static void display(Enumeration<NetworkInterface> nifs) 
                                throws SocketException
    {
        while (nifs.hasMoreElements())
        {
            NetworkInterface nif = nifs.nextElement();
            
            System.out.printf("%s (%s)\n", 
                              nif.getDisplayName(), nif.getName());

            Enumeration<InetAddress> addresses = nif.getInetAddresses();
            while (addresses.hasMoreElements())
            {
                System.out.printf("\t%s\n", addresses.nextElement());
            }
            System.out.println();
        }
    }
}
        

• Hardware-Related:
  • getHardwareAddress() returns the hardware (e.g., MAC for Ethernet) address
• Other Properties:
  • getMTU() returns the maximum transmision unit
  • isLoopback()
  • isUp()
  • isVirtual()
  • supportsMulticast()