Sams Teach Yourself C in 21 Days

applicationsare programs that run on their own, just like the C programs you have seen

throughout this book. Java can be used in a number of ways. Java applets use to receive a

lot of attention because of all the hype surrounding the Web. Java can also be used to cre-

ate components, server-side Web applications, and enterprise-level objects. Most impor-

tantly, Java is useful for creating stand-alone applications. In this brief introduction to

Java, you will concentrate on using Java for stand-alone applications, as that is more

directly comparable to the uses of C and C++ you have seen elsewhere in this book.

Java Program Essentials ......................................................................................

At the most simple level, a Java program consists of two parts, one contained within the

other. As with just about everything else in Java, a program is a class and is defined as

follows:

public class ProgramName

{

}

All the code that makes up the program is placed within the braces, and the entire source

code file is saved on disk with an extension of java. A program called ProgramName

would be stored as ProgramName.java. The second essential part of a Java program is

themainfunction. When you execute a Java program, execution starts in mainjust as it

does in C and C++. Here’s what mainlooks like:

public class ProgramName {

public static void main (String args[])

{

}

}

You’ll note that maintakes an argument called args[]. This is the way that command

line arguments are passed to a Java program. Unlike C, you don’t have an integer argc

variable stating how many values were provided. Instead, you use args.length.

Working with Imports ..................................................................................

Almost every Java program, except the simplest, must use the importstatement to have

access to classes that the program uses. You must use importwith classes that are part of

Java, as well as with classes you have written. importstatements are placed at the start

of a Java source code file, before the class definition. You can import classes individual-

ly, as in this example that imports the class someClassfrom the package my.package:

import my.package.someClass;

704 Bonus Day 4

39 448201x-Bonus4 8/13/02 11:19 AM Page 704