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,
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.
}
}
Type all code, commands, and file names exactly as shown. Both the compiler (javac) and launcher tool (java) are case-sensitive, so you must capitalize consistently.
|
helloworldappSave 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:
- Using the Save in combo box, specify the folder (directory) where you’ll save your file. In this example, the directory is java on the C drive.
- In the File name text field, type
"HelloWorldApp.java", including the quotation marks. - From the Save as type combo box, choose Text Documents (*.txt).
- In the Encoding combo box, leave the encoding as ANSI.
When you’re finished, the dialog box should look like this.
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 Command Prompt (Windows XP), or by choosing Run… and then entering cmd. The shell window should look similar to the following figure.
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 java on the C drive, type the following command at the prompt and press Enter:
cd C:java
Now the prompt should change to C:\java>.
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 java directory on the D drive, you must enter D:, as shown in the following figure.
Changing directory on an alternate drive.
If you enter
dir at the prompt, you should see your source file, as the following figure shows.
Directory listing showing the .java source file.
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 shown in the following figure.
Directory listing, showing the generated .class file
Now that you have a .class file, you can run your program.
Run the Program
In the same directory, enter the following command at the prompt:
java HelloWorldApp
The next figure shows what you should now see:
The program prints “Hello World!” to the screen.
Congratulations! Your program works!
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Bhuvana Sundaramoorthy\'s Blog 
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Hi, ur blog is really informative and easy for freshers(like me) to understand java.
Wanna learn more from you bhuvana..
hi
i’m starting to learn JAVA but i have no idea what i’m doing.
I’m using Borland JAVAbuilder but i have problems.
can youu tell me where to start.
thanks
learning java is so easy,for that u have to put some effort .just download the simple programs and work it…..and read the proper books dont compare more books……create programs of ur own….all the best
Bhuvana,
Great Work..It wud really be helpful if you cud also post information on execution stages of scripting languages like JavaScript,WSH,VB Script and Python etc.
How does a script execute when run on a machine…
great work,,simple explanation..Thank u.
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Hello Bhuvana,
I just happened to pass by your blog, found it very good & started to work on its steps to learn java programming. But after entering the compile command I ended up with the following error message, ‘javac’ is not recognized as an internal or external command, operable program or batch file.
great work,
HeArtfull Thanks.
goog
Thanks friend,is very informative for learner…………
When you are so used to IDE’s, sometimes you don’t know how to run Java program from command line. Nice to have refreshed my knowledge =)
This is very interesting and nice to read, I like the interesting article … good luck salam sukses
This is very interesting and nice to read, I like the interesting article … good luck salam sukses..Mampir Ya Gan
Very helpful tutorial to create first application in Java.
Great Work..It wud really be helpful if you cud also post information on execution stages of scripting languages like JavaScript,WSH,VB Script and Python etc.
How does a script execute when run on a machine…
pagi
Good tutorial
Hi am a java learner. can i write java programs in jdeveloper?
if i wrote that in jdev how can i compile it in java?
can u tell me the process