Java Coffee Break Newsletter Volume 1 Issue 02

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Java Coffee Break Newsletter

 · 9 months ago

                Java Coffee Break Newsletter Vol 1, Issue 2 
                             ISSN 1442-3790 

 Welcome to the second Java Coffee Break Newsletter! This issue comes 
 a little early, due to the large number of subscribers in the last 
 week, and because of the new tutorial that is now available. 

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Java Coffee Break Updates 

 * New tutorial 
 * JDK 1.2 Booklist 
 * Free access to the latest resources from Sun 

 
1. New tutorial 
  
   Learn the basics of network programming in Java, with the latest in 
   our series of tutorials aimed at beginners. Network programming can 
   be easy, and this tutorial will show you how to write Java clients.  
   A brief excerpt from the tutorial is included later in the  
   newsletter. 

   If networking is a little too advanced for now, try some of the 
   other tutorials, which teach Java right from the beginning. 

   All our Java tutorials can be found at 
   http://www.davidreilly.com/jcb/tutorials.html 

2. JDK 1.2 Booklist 

   If you haven't been following the latest news from Sun, you may 
   not be aware that a new version of the Java Developers Kit (JDK) 
   is coming. JDK1.2 includes many new features, including support 
   for servlets, swing, collections and more. 

   If you're interested in getting up to speed with these 
   technologies, I've put together a booklist of some JDK1.2 titles. 
   You can find the list at  
   http://www.davidreilly.com/jcb/books/jdk1.2/ 

3. Free access to the latest resources from Sun 

   Sun's Java Developer Connection (JDC) offers developers early 
   access to software and toolkits (including early betas of JDK). 
   It's free, and helps you keep up to date. 

   Join JDC at http://java.sun.com/jdc/ 

 
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Java 109 - Networking with Java 

In this tutorial, we'll cover networking with Java. Don't worry if 
you're not familiar with networking - this will be only a brief 
introduction. We'll examine some of the classes in the java.net 
package, and show you how to write a simple network client in Java. 
First, however, we need to cover some background theory. 

 
How do computers talk to each other via the Internet? 

The Internet is composed of millions of computers, located all across 
the globe, communicating and transmitting information over a variety 
of computing systems, platforms, and networking equipment.  Each of 
these computers (unless they are connecting via an intranet) will 
have a unique IP address. 

IP addresses are 32-bit numbers, containing four octets (8 bit numbers) 
separated by a full stop. Each computer with a direct internet 
connection will have a unique IP address, (e.g. 207.68.156.61). Some 
computers have temporary addresses, such as when you connect to your 
ISP through a modem. Others have permanent addresses, and some even 
have their own unique domain names (e.g. www.microsoft.com). 

An IP address allows us to uniquely identify a device or system 
connected to the Internet. If I wanted to connect to a specific IP 
address, and send a message, I could do so. Without an IP address, my 
message would have no way of reaching its destination - a bit like 
leaving the address off a letter or parcel. 

 
Internet Addressing with Java 

Handling internet addresses (domain names, and IP addresses) is made 
easy with Java. Internet addresses are represented in Java by the 
InetAddress class. InetAddress provides simple methods to convert 
between domain names, and numbered addresses. 

We start by importing the java.net package, which contains a set of 
pre-written networking classes (including InetAddress). 

      import java.net.*; 

Next, we declare a new variable of type InetAddress, which we assign 
the value of the local host machine (for machines not connected to a 
network, this should represent 127.0.0.1). Due to the fact that 
InetAddresses can generate exceptions, we must place this code between 
a try .. catch UnknownHostException block. 

       // Obtain the InetAddress of the computer on which this program 
       // is running 
       InetAddress localaddr = InetAddress.getLocalHost(); 

The InetAddress class has methods that return the IP address as an  
array of bytes (which can be easily converted into a string), as well 
as a string representation of its domain name (e.g. mydomain.org ). We 
can print out the InternetAddress, as well as the domain name of the local 
address.  

       System.out.println ("Local IP Address : " + localaddr ); 
       System.out.println ("Local hostname : " + localaddr.getHostName()); 

The full tutorial, including downloadable source code, is available at 
http://www.davidreilly.com/jcb/java109/java109.html 

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