1.2 The "Hello World!" Application

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The sections listed below provide detailed instructions for compiling and running a simple "Hello World!" application. The first section provides information on getting started with the NetBeans IDE, an integrated development environment that greatly simplifies the software development process. The NetBeans IDE runs on all of the platforms listed below. The remaining sections provide platform-specific instructions for getting started without an integrated development environment. If you run into problems, be sure to consult the common problems section; it provides solutions for many issues encountered by new users.

"Hello World!" for the NetBeans IDE These instructions are for users of the NetBeans IDE. The NetBeans IDE runs on the Java platform, which means that you can use it with any operating system for which there is a JDK 7 available. These operating systems include Microsoft Windows, Solaris OS, Linux, and Mac OS X. We recommend using the NetBeans IDE instead of the command line whenever possible.

"Hello World!" for Microsoft Windows These command-line instructions are for users of Windows XP Professional, Windows XP Home, Windows Server 2003, Windows 2000 Professional, and Windows Vista.

"Hello World!" for Solaris OS and Linux These command-line instructions are for users of Solaris OS and Linux. Common Problems (and Their Solutions) Consult this page if you have problems compiling or running your application.



1. "Hello World!" for the NetBeans IDE


It's time to write your first application! These detailed instructions are for users of the NetBeans IDE. The NetBeans IDE runs on the Java platform, which means that you can use it with any operating system for which there is a JDK available. These operating systems include Microsoft Windows, Solaris OS, Linux, and Mac OS X.


  • A Checklist

To write your first program, you'll need:

1. The Java SE Development Kit (JDK 7 has been selected in this example)
  • For Microsoft Windows, Solaris OS, and Linux: Java SE Downloads Index page
  • For Mac OS X: developer.apple.com
2. The NetBeans IDE

For all platforms: NetBeans IDE Downloads Index page

Creating Your First Application

Your first application, HelloWorldApp, will simply display the greeting "Hello World!" To create this program, you will:

  • Create an IDE project 
    • When you create an IDE project, you create an environment in which to build and run your applications. Using IDE projects eliminates configuration issues normally associated with developing on the command line. You can build or run your application by choosing a single menu item within the IDE.
  • Add code to the generated source file
    • A source file contains code, written in the Java programming language, that you and other programmers can understand. As part of creating an IDE project, a skeleton source file will be automatically generated. You will then modify the source file to add the "Hello World!" message.
  • Compile the source file into a .class file
    • The IDE invokes the Java programming language compiler (javac), which takes your source file and translates its text into instructions that the Java virtual machine can understand. The instructions contained within this file are known as bytecodes.
  • Run the program
    • The IDE invokes the Java application launcher tool (java), which uses the Java virtual machine to run your application.
Creating Your First Application


    • Create an IDE Project

To create an IDE project:

1. Launch the NetBeans IDE.
    • On Microsoft Windows systems, you can use the NetBeans IDE item in the Start menu.
    • On Solaris OS and Linux systems, you execute the IDE launcher script by navigating to the IDE's bin directory and typing ./netbeans.
    • On Mac OS X systems, click the NetBeans IDE application icon.
2. In the NetBeans IDE, choose File | New Project....

The "Hello World!" Application

NetBeans IDE with the File | New Project menu item selected.

3. In the New Project wizard, expand the Java category and select Java Application as shown in the following figure:

The "Hello World!" Application

NetBeans IDE, New Project wizard, Choose Project page.

4. In the Name and Location page of the wizard, do the following (as shown in the figure below):
    • In the Project Name field, type Hello World App.
    • In the Create Main Class field, type helloworldapp.HelloWorldApp.

The "Hello World!" Application

NetBeans IDE, New Project wizard, Name and Location page.

5. Click Finish.

The project is created and opened in the IDE. You should see the following components:

  • The Projects window, which contains a tree view of the components of the project, including source files, libraries that your code depends on, and so on.
  • The Source Editor window with a file called HelloWorldApp.java open.
  • The Navigator window, which you can use to quickly navigate between elements within the selected class.
The "Hello World!" Application

NetBeans IDE with the HelloWorldApp project open.


    • Add JDK 8 to the Platform List (if necessary)

It may be necessary to add JDK 8 to the IDE's list of available platforms. To do this, choose Tools | Java Platforms as shown in the following figure:

The "Hello World!" Application

Selecting the Java Platform Manager from the Tools Menu

If you don't see JDK 8 (which might appear as 1.8 or 1.8.0) in the list of installed platforms, click Add Platform, navigate to your JDK 8 install directory, and click Finish. You should now see this newly added platform:

The "Hello World!" Application

The Java Platform Manager

To set this JDK as the default for all projects, you can run the IDE with the --jdkhome switch on the command line, or by entering the path to the JDK in the netbeans_j2sdkhome property of your INSTALLATION_DIRECTORY/etc/netbeans.conf file.

To specify this JDK for the current project only, select Hello World App in the Projects pane, choose File | Project Properties (Hello World App), click Libraries, then select JDK 1.8 in the Java Platform pulldown menu. You should see a screen similar to the following:

The "Hello World!" Application

The IDE is now configured for JDK 8.

    • Add Code to the Generated Source File

When you created this project, you left the Create Main Class checkbox selected in the New Project wizard. The IDE has therefore created a skeleton class for you. You can add the "Hello World!" message to the skeleton code by replacing the line:

// TODO code application logic here
with the line:

System.out.println("Hello World!"); // Display the string.
Optionally, you can replace these four lines of generated code:

/**
 *
 * @author
 */
with these lines:

/**
 * The HelloWorldApp class implements an application that
 * simply prints "Hello World!" to standard output.
 */
These four lines are a code comment and do not affect how the program runs. Later sections of this tutorial explain the use and format of code comments.

Be Careful When You Type uppercase letter A   lowercase letter a

Note: Type all code, commands, and file names exactly as shown. Both the compiler (javac) and launcher (java) are case-sensitive, so you must capitalize consistently.

HelloWorldApp is not the same as helloworldapp.
Save your changes by choosing File | Save.

The file should look something like the following:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package helloworldapp;

/**
 * The HelloWorldApp class implements an application that
 * simply prints "Hello World!" to standard output.
 */
public class HelloWorldApp {

   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }

}
    • Compile the Source File into a .class File

To compile your source file, choose Run | Build Project (Hello World App) from the IDE's main menu.

The Output window opens and displays output similar to what you see in the following figure:

The "Hello World!" Application

Output window showing results of building the HelloWorld project.

If the build output concludes with the statement BUILD SUCCESSFUL, congratulations! You have successfully compiled your program!

If the build output concludes with the statement BUILD FAILED, you probably have a syntax error in your code. Errors are reported in the Output window as hyperlinked text. You double-click such a hyperlink to navigate to the source of an error. You can then fix the error and once again choose Run | Build Project.

When you build the project, the bytecode file HelloWorldApp.class is generated. You can see where the new file is generated by opening the Files window and expanding the Hello World App/build/classes/helloworldapp node as shown in the following figure.

The "Hello World!" Application

Files window, showing the generated .class file.

Now that you have built the project, you can run your program.

    • Run the Program

From the IDE's menu bar, choose Run | Run Main Project.

The next figure shows what you should now see.

The "Hello World!" Application

The program prints "Hello World!" to the Output window (along with other output from the build script).


2. "Hello World!" for Microsoft Windows



It's time to write your first application! The following instructions are for users of Windows Vista, Windows 7, and Windows 8. Instructions for other platforms are in "Hello World!" for Solaris OS and Linux and "Hello World!" for the NetBeans IDE.

If you encounter problems with the instructions on this page, consult the Common Problems (and Their Solutions).

  • A Checklist
To write your first program, you'll need:

1. The Java SE Development Kit 8 (JDK 8)

You can download the Windows version now. (Make sure you download the JDK, not the JRE.) Consult the installation instructions.

2. A text editor

In this example, we'll use Notepad, a simple editor included with the Windows platforms. You can easily adapt these instructions if you use a different text editor.

These two items are all you'll need to write your first application.

  • Creating Your First Application
Your first application, HelloWorldApp, will simply display the greeting "Hello world!". To create this program, you will: 

  • Create a source file
    • A source file contains code, written in the Java programming language, that you and other programmers can understand. You can use any text editor to create and edit source files.
  • Compile the source file into a .class file
    • The Java programming language compiler (javac) takes your source file and translates its text into instructions that the Java virtual machine can understand. The instructions contained within this file are known as bytecodes.
  • Run the program
    • The Java application launcher tool (java) uses the Java virtual machine to run your application.

    • Create a Source File

To create a source file, you have two options:

You can save the file HelloWorldApp.java on your computer and avoid a lot of typing. Then, you can go straight to Compile the Source File into a .class File.

Or, you can use the following (longer) instructions.

First, start your editor. You can launch the Notepad editor from the Start menu by selecting Programs > Accessories > Notepad. In a new document, type in the following code:

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

Be Careful When You Type uppercase letter A   lowercase letter a

Note: Type all code, commands, and file names exactly as shown. Both the compiler (javac) and launcher (java) are case-sensitive, so you must capitalize consistently.

HelloWorldApp is not the same as helloworldapp.
Save the code in a file with the name HelloWorldApp.java. To do this in Notepad, first choose the File > Save As menu item. Then, in the Save As dialog box:
  1. Using the Save in combo box, specify the folder (directory) where you'll save your file. In this example, the directory is myapplication on the C drive.
  2. In the File name text field, type "HelloWorldApp.java", including the quotation marks.
  3. From the Save as type combo box, choose Text Documents (*.txt).
  4. In the Encoding combo box, leave the encoding as ANSI.
When you're finished, the dialog box should look like this.

The "Hello World!" Application

The Save As dialog just before you click Save.

Now click Save, and exit Notepad.

    • Compile the Source File into a .class File

Bring up a shell, or "command," window. You can do this from the Start menu by choosing Run... and then entering cmd. The shell window should look similar to the following figure.

The "Hello World!" Application

A shell window.

The prompt shows your current directory. When you bring up the prompt, your current directory is usually your home directory for Windows XP (as shown in the preceding figure.

To compile your source file, change your current directory to the directory where your file is located. For example, if your source directory is myapplication on the C drive, type the following command at the prompt and press Enter:

cd C:\myapplication
Now the prompt should change to C:\myapplication>.

Note
To change to a directory on a different drive, you must type an extra command: the name of the drive. For example, to change to the myapplication directory on the D drive, you must enter D:, as follows:

C:\>D:

D:\>cd myapplication

D:\myapplication>
If you enter dir at the prompt, you should see your source file, as follows:

C:\>cd myapplication

C:\myapplication>dir
 Volume in drive C is System
 Volume Serial Number is F2E8-C8CC

 Directory of C:\myapplication

2014-04-24  01:34 PM    <DIR>          .
2014-04-24  01:34 PM    <DIR>          ..
2014-04-24  01:34 PM               267 HelloWorldApp.java
               1 File(s)            267 bytes
               2 Dir(s)  93,297,991,680 bytes free

C:\myapplication>
Now you are ready to compile. At the prompt, type the following command and press Enter.

javac HelloWorldApp.java
The compiler has generated a bytecode file, HelloWorldApp.class. At the prompt, type dir to see the new file that was generated as follows:

C:\myapplication>javac HelloWorldApp.java

C:\myapplication>dir
 Volume in drive C is System
 Volume Serial Number is F2E8-C8CC

 Directory of C:\myapplication

2014-04-24  02:07 PM    <DIR>          .
2014-04-24  02:07 PM    <DIR>          ..
2014-04-24  02:07 PM               432 HelloWorldApp.class
2014-04-24  01:34 PM               267 HelloWorldApp.java
               2 File(s)            699 bytes
               2 Dir(s)  93,298,032,640 bytes free

C:\myapplication>
Now that you have a .class file, you can run your program.

If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).

    • Run the Program

In the same directory, enter the following command at the prompt:

java -cp . HelloWorldApp
You should see the following on your screen:

C:\myapplication>java -cp . HelloWorldApp
Hello World!

C:\myapplication>

If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).


3. "Hello World!" for Solaris OS and Linux



It's time to write your first application! These detailed instructions are for users of Solaris OS and Linux. Instructions for other platforms are in "Hello World!" for Microsoft Windows and "Hello World!" for the NetBeans IDE.

If you encounter problems with the instructions on this page, consult the Common Problems (and Their Solutions).

  • A Checklist


To write your first program, you'll need:

1. The Java SE Development Kit 8 (JDK 8)

You can download the Solaris OS or Linux version now. (Make sure you download the JDK, not the JRE.) Consult the installation instructions.

2. A text editor

In this example, we'll use Pico, an editor available for many UNIX-based platforms. You can easily adapt these instructions if you use a different text editor, such as vi or emacs.

These two items are all you'll need to write your first application.
  • Creating Your First Application
Your first application, HelloWorldApp, will simply display the greeting "Hello world!". To create this program, you will:
  • Create a source file
    • A source file contains code, written in the Java programming language, that you and other programmers can understand. You can use any text editor to create and edit source files.
  • Compile the source file into a .class file
    • The Java programming language compiler (javac) takes your source file and translates its text into instructions that the Java virtual machine can understand. The instructions contained within this .class file are known as bytecodes.
  • Run the program
    • The Java application launcher tool (java) uses the Java virtual machine to run your application.

    • Create a Source File

To create a source file, you have two options:
  • You can save the file HelloWorldApp.java on your computer and avoid a lot of typing. Then, you can go straight to Compile the Source File.
  • Or, you can use the following (longer) instructions.
First, open a shell, or "terminal," window.

The "Hello World!" Application

A new terminal window.

When you first bring up the prompt, your current directory will usually be your home directory. You can change your current directory to your home directory at any time by typing cd at the prompt and then pressing Return.

The source files you create should be kept in a separate directory. You can create a directory by using the command mkdir. For example, to create the directory examples/java in the /tmp directory, use the following commands:

cd /tmp
mkdir examples
cd examples
mkdir java

To change your current directory to this new directory, you then enter:

cd /tmp/examples/java
Now you can start creating your source file.

Start the Pico editor by typing pico at the prompt and pressing Return. If the system responds with the message pico: command not found, then Pico is most likely unavailable. Consult your system administrator for more information, or use another editor.

When you start Pico, it'll display a new, blank buffer. This is the area in which you will type your code.

Type the following code into the new buffer:

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

Be Careful When You Type uppercase letter A   lowercase letter a

Note: Type all code, commands, and file names exactly as shown. Both the compiler (javac) and launcher (java) are case-sensitive, so you must capitalize consistently.

HelloWorldApp is not the same as helloworldapp.

Save the code in a file with the name HelloWorldApp.java. In the Pico editor, you do this by typing Ctrl-O and then, at the bottom where you see the prompt File Name to write:, entering the directory in which you wish to create the file, followed by HelloWorldApp.java. For example, if you wish to save HelloWorldApp.java in the directory /tmp/examples/java, then you type /tmp/examples/java/HelloWorldApp.java and press Return.

You can type Ctrl-X to exit Pico.

    • Compile the Source File into a .class File

Bring up another shell window. To compile your source file, change your current directory to the directory where your file is located. For example, if your source directory is /tmp/examples/java, type the following command at the prompt and press Return:

cd /tmp/examples/java
If you enter pwd at the prompt, you should see the current directory, which in this example has been changed to /tmp/examples/java.

If you enter ls at the prompt, you should see your file.

The "Hello World!" Application

Results of the ls command, showing the .java source file.

Now are ready to compile the source file. At the prompt, type the following command and press Return.

javac HelloWorldApp.java

The compiler has generated a bytecode file, HelloWorldApp.class. At the prompt, type ls to see the new file that was generated: the following figure.

The "Hello World!" Application

Results of the ls command, showing the generated .class file.

Now that you have a .class file, you can run your program.

If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).

If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).

    • Run the Program

In the same directory, enter at the prompt:

java HelloWorldApp

The next figure shows what you should now see.

The "Hello World!" Application

The output prints "Hello World!" to the screen.

If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).

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