Java HowTo Guide

Information in a java program is organized in a specific way. The smallest and simplest java program can only execute if it is coded as a .java file. When a .java file is created, it must contain at least one class. A java class contains specific information such as variables and methods. A single java file is generally structured similarly:

public class Greeting

{

int someVar = 0;

public static void main(String[] args) {

System.out.println(“Hello, world!”);

}

}

In this classic “Hello, world!” output, the class Greeting is defined. A .java file must contain and define at least one class. A class can be controlled by methods defined within it. In this example, a special method main will try to show the output “Hello, world!” when the class is loaded. A class may contain fields such as the integer type of variable declared as someVar, with the value of zero. As each .java file should have one class, it should also have one class that has the main method. Greeting, someVar, and main are called identifiers. An identifier labels entities in a java program such as a class, a variable, or a method. The class Greeting is a public class. Each java file can have many classes but only one can be declared public. Note also that the method main is public, and static.

Many .java files may be actually needed to run a more complex program. Similarly, some methods and classes are meant to be reused in some other way for various programming applications. In this case, it is best to organize .java files according to their use, and group programs that generally work for the same kind of output. If a greetprogram.java file contains:

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