The JavaTM Tutorial

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Trail: Getting Started
Lesson: The "Hello World" Application

## The Anatomy of a Java Application

> Now that you've seen a Java application (and perhaps even compiled and run it), you might be wondering how it works and how similar it is to other Java applications. Remember that a Java application is a standalone Java program-- a program written in the Java language that runs independently of any browser.

> > Note: If you couldn't care less about Java applications, you're already familiar with object-oriented concepts, and you understand the Java code you've seen so far, feel free to skip ahead to Writing Applets.

> This section dissects the "Hello World" application you've already seen. Here, again, is its code:

> >     /**
> >      * The HelloWorldApp class implements an application that
> >      * simply displays "Hello World!" to the standard output.
> >      */
> >     class HelloWorldApp {
> >         public static void main(String[] args) {
> >             System.out.println("Hello World!"); //Display the string.
> >         }
> >     }

### Comments in Java Code

> The "Hello World" application has two blocks of comments. The first block, at the top of the program, uses `/**` and `*/` delimiters. Later, a line of code is explained with a comment that's marked by `//` characters. The Java language supports a third kind of comment, as well -- the familiar C-style comment, which is delimited with `/*` and `*/`. Comments in Java Code further explains the three forms of comments that the Java language supports.

### Defining a Class

> In the Java language, each method (function) and variable exists within a class or an object (an instance of a class). The Java language does not support global functions or variables. Thus, the skeleton of any Java program is a class definition. Defining a Class gives you more information.

### The `main` Method

> The entry point of every Java application is its `main` method. When you run an application with the Java interpreter, you specify the name of the class that you want to run. The interpreter invokes the `main` method defined within that class. The `main` method controls the flow of the program, allocates whatever resources are needed, and runs any other methods that provide the functionality for the application. The `main` Method tells you more.

### Using Classes and Objects

> The other components of a Java application are the supporting objects, classes, methods, and Java language statements that you write to implement the application. Using Classes and Objects introduces you to these components.

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