Java Coffee Break Newsletter Volume 1 Issue 03

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Java Coffee Break Newsletter

 · 10 months ago

                Java Coffee Break Newsletter Vol 1, Issue 3 
                             ISSN 1442-3790 

 Welcome to the third Java Coffee Break Newsletter. This issue has 
 some information about Swing, free offers from the Java Lobby, and 
 two new Q&A articles. Enjoy! 

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Java Coffee Break Updates 

 * Java Tutorials 
 * Free offers - Join the Java Lobby 
 * Swing/JFC namespace news 
 * Q&A : How can I generate random numbers? 
 * Q&A : What's the difference between = & ==? 

1. Java Tutorials 
  
   If you're new to the Java programming language, and need a little 
   help, then try some of the free tutorials available from the 
   Java Coffee Break. These aren't your normal tutorials - they don't 
   require extensive Java experience or knowledge. 

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

 
2. Free offers - Join the Java Lobby 

   The Java Lobby is an independent group of Java software developers. 
   They help promote the Java language, and offer benefits and 
   special promotions to their members. Membership is free! 

   Recent offers include a free subscription to Java Developer's 
   Journal, and a copy of ZeroG's InstallAnywhere tool. For more 
   details, check out http://www.javalobby.org/ 

 
3. Swing/JFC namespace news 

   For developers who have used the Swing / Java Foundation Classes 
   you may have been surprised to find that the package names have 
   changed in Java 1.2. A new proposal, to place swing in a new 
   javax.swing package has been made. For more information, see 
   Sun's statement at 

   http://java.sun.com/products/jfc/package.html 

 
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Q&A : How can I generate random numbers? 

Generating random numbers is simple. Provided as part of the java.util 
package, the Random class makes it easy to generate numbers.  

Start by creating an instance of the Random class  

 // Create an instance of the random class 
 Random r = new Random(); 

Now, you must request a number from the generator. Supposing we 
wanted an integer number, we'd call the nextInt() method. 

 // Get an integer 
 int number = r.nextInt(); 

Often you'll want numbers to fall in a specific range (for example, 
from one to ten). We can use the modulus operator to limit the range of 
the numbers. This will give us the remainder of the number when divided 
by ten (giving us a range -9 to +9). To eliminate negative numbers, if  
the number is less than one we'll add ten to it. This gives us random 
numbers between one and ten!  
  
 // Accept only up to ten 
 int random_number = number % 10; 
 if (random_number < 1) random_number = random_number + 10; 

Creating random numbers in an application or applet really isn't that 
difficult. Just remember to limit the range of your numbers, and to 
import the java.util.Random class. 

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Q&A : What's the difference between = & ==? 

One of the most common programming mistakes that one can make is to 
confuse the equal sign (=) with a double equal sign (==). While 
experienced programmers can still make the same mistake, knowing the 
difference between the two is a good way to avoid it. 

When we wish to assign a value to a variable or member, we use the 
equals sign (=). As an example, the following would assign the  
value of three to the variable a. 

 a = 1 + 2; // assignment operation 

When we wish to make a comparison, such as in an if statement, we use 
the double equals sign (==). A simple example would be the 
following 

 if ( a == b ) then System.out.println ("Match found!"); 

Now consider what would have happened if we used an assignment 
operator instead. A would be assigned the value of B - destroying 
the current contents of A and giving us an incorrect comparison. 
Finding this type of error can be difficult, because the two 
operators look so similar. So why does Java use such confusing  
operators? Java draws its roots from C, which shares the same  
problem. Unfortunately, its something that all Java programmers must 
learn to live with. 

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