Physics Simulation       Lecture 13B Networking Internet Basics IP - Datagrams TCP - UDP Application Layer Ports Java Networking URL InetAddress Sockets Client-Server RMI Exercises Lectures 1A: Introduction 1B: Java Intro 2A: BuildingBlocks 2B: Objects 3A: More Objects 3B: Exceptions        & Threads 4A: Waves 4B: Nuclear &        Particle 5A: AWT 5B: More AWT       & Graphics 6A:Detectors &       Simulation 6B: LHC/Atlas &      RandomSims     7A: Swing 7B: Java2D 8A: Java Apps 8B: Dialogs &     MoreClasses 9A: Java I/O 9B: Utilities,         Unicode 10A: More     Threading 10B: File     Handling 11A: Array,Print,     Images 11B: SimplePhysics     Simulation 12A: Tips &     Techniques 12B: More Tips &     Techniques 13A: Satellite     Simulations 13B: Intro to Java     Networking 14A: Java Servers 14B: HTTP Server 15A: ServerClient 15B: ServerClient    Expt.Simulation 16A: Course           Review 16B: ExerciseTest         Discussion     Contacts     Description     Exercises     Index     Outline     Q&A     Resources     StudentInfoForm     Student Pages     What's New

Home : Lectures : Lecture 13B : InetAddress InetAddress The java.net.InetAddress class represents IP addresses. It works with the host name (String) and IP address (int) of an Internet host. InetAddress has several useful methods for obtaining host names and IP addresses. Here are some demos, some derived from those in the book Java Network Programming, by E. R. Harold. The first one shows how to get the IP address from the host name or, vice versa, the host name from the IP address. Note that getByName(String str) returns the HostName/IP_Address pair given either the host name or the IP address: oreilly.java   import java.net.*; class oreilly {   public static void main (String args[]) {     InetAddress address=null;     System.out.println("From Domain name:");     try {       address = InetAddress.getByName("www.oreilly.com");       System.out.println(         "  InetAddress for www.oreilly.com = "+address);     }     catch (UnknownHostException e) {       System.out.println("  Could not find www.oreilly.com");       System.exit(0);     }     String IPstr="host address string.";     System.out.println("From IP number:");     try {       IPstr = address.getHostAddress();       address = InetAddress.getByName(IPstr);       System.out.println(         "  InetAddress for "+IPstr+" = "+address);     }     catch (UnknownHostException e) {       System.out.println("  Could not find "+IPstr);     }   } } Here get the local host name and IP address: myAddress.java   > java myAddress   This computer's address = foo/130.237.217.62   import java.net.*; class myAddress {   public static void main (String args[]) {     try {       InetAddress address =                      InetAddress.getLocalHost();       System.out.println("This computer's address = " +address);     } catch (UnknownHostException e) {       System.out.println(         "Could not find this computer's address.");     }   } } This applet presents the local host and IP address: MyAddressApplet.java mport java.net.*; public class MyAddressApplet extends java.applet.Applet {    String msg;    private InetAddress myAddress = null; /*--------------------------------------------------------*/   public void init(){     try{       myAddress = InetAddress.getLocalHost();       msg = "Local IP address = " + myAddress.toString();     } catch (UnknownHostException e){       System.out.println("Failed to getLocalHost");       msg = "Local IP address is unknown";     }   } /*---------------------------------------------------------*/   public void paint (java.awt.Graphics g){     g.drawString(Msg, 10, 15);   } }   Finally, this application returns the IP address if given a host name, or returns the host name if given the IP address: GetAddress.java   import java.net.*; class GetAddress {   public static void main (String args[]) {     // Check on argument     if( args.length != 1){       System.out.println("Need IP or Host name argument!");       System.exit(0);     }     try {       InetAddress address = InetAddress.getByName(args[0]);       System.out.println("This computer's address = " + address);     }     catch (UnknownHostException e) {       System.out.println(        "Could not find this computer's address.");     }   } }

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