The JavaTM Tutorial
Previous Page Lesson Contents Next Page Start of Tutorial > Start of Trail > Start of Lesson Search
Feedback Form

Trail: Getting Started
Lesson: Your First Cup of Java

Your First Cup of Java (for Mac OS)

Detailed Instructions
for Your First Program

The following instructions will help you write your first Java program. These instructions are for users of the Mac OS platform.
1. A Checklist 2. Creating Your First Application
     a. Create a Java Source File
     b. Compile the Source File
     c. Run the Program
3. Creating Your First Applet 4. Where to Go from Here

Your feedback is important to us! If you have comments about these instructions, send them to: tutorial@java.sun.com. In your message, put cup of java in the subject header. This page was adapted for Mac OS by tutorial reader Werner van Mook.


1. A Checklist 

To write your first program, you will need:
  1. A development environment for the Java platform. You can download(outside of the tutorial) the Macintosh Runtime Environment for Java Software Development Kit (MRJ SDK) from Apple's website.
  2. A runtime environment for the same version of the Java platform. You can download(outside of the tutorial) the Macintosh Runtime Enviroment for Java (MRJ) from Apple's website.
  3. A text editor. In this example, we'll use SimpleText, the simple editor included with the Mac OS platforms. To find SimpleText, from the File menu select Find, type in "SimpleText", and then hit the Find button. You might find more then one SimpleText application; any one of them should work fine. You can easily adapt these instructions if you use a different text editor.
These three items are all you need to write your first Java program.

2. Creating Your First Application
 
Why Bytecodes are Cool

So, you've heard that with the Java programming language, you can "write once, run anywhere." This means that when you compile your program, you don't generate instructions for one specific platform. Instead, you generate Java bytecodes, which are instructions for the Java Virtual Machine (Java VM). If your platform--whether it's Win32, UNIX, Mac OS, or an Internet browser--has the Java VM, it can understand those bytecodes.

 
Your first program, HelloWorldApp, will simply display the greeting "Hello world!". To create this program, you will: 
  • Create a Java source file. A source file contains text, 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 bytecode file. The Java compiler, javac, takes your source file and translates its text into instructions that the Java Virtual Machine (Java VM) can understand. The compiler puts these instructions into a bytecode file.
     
  • Run the program contained in the bytecode file. The Java VM is implemented by a Java interpreter, java. This interpreter takes your bytecode file and carries out the instructions by translating them into instructions that your computer can understand.

top

a. Create a Java Source File.

You have two options:

  • You can save the file HelloWorldApp.java(in a .java source file) on your computer and avoid a lot of typing. Then, you can go straight to step b.

  • Or, you can follow these (longer) instructions:

1. Start SimpleText. In a new document, type in the following code:

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

Type all code, commands, and file names exactly as shown. The Java compiler and interpreter are case-sensitive, so you must capitalize consistently.

HelloWorldApp  helloworldapp
2. Save this code to a file. From the menu bar, select File > Save As. In the Save As dialog box: 
    • Specify the folder where you'll save your file. In this example, the folder is MRJ SDK 2.1. 
    • In the Save this document as: text box, type HelloWorldApp.java.
When you're finished, the dialog box should look like this:

Now click Save, and exit SimpleText.

top

b. Compile the Source File.

Go to the folder MRJ SDK 2.1 and it should look something like this:

There will be a folder called Tools. In this folder there is a folder called MRJTools.
Open it. You will see a program called javac.

Now drag and drop your HelloWorldApp.java onto this Javac application. Javac will now open and should show you:

In the box Source Files it gives you the absolute path to the java file we just created. For now we do not have to do anything else except clicking on the Do Javac button.

If you do not get any error messages, congratulations. You have successfully compiled your program.

 
Error Explanation

If you drag and drop your .java file on top of the javac program and the file is moved on top of the javac application.

When you tried this and the only thing that happens is your .java file gets copied/moved on top of your javac application you have to rebuild your desktop.

To do this you have to restart you computer and press and hold both the "Apple" - and "Alt" key until you get a window asking you if you really want to rebuild your desktop.

Answer with yes. When your computer is finished you should be able to drag and drop the .java file on to javac.


The compiler has generated a Java bytecode file, HelloWorldApp.class. Look in the same folder where you saved the .java file and you will see the .class file.

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

top

c. Run the Program.

In the MRJ SDK 2.1 folder there is a folder called JBindery. Open this folder and there should be an application called JBindery.

Drag and drop the HelloWorldApp.class file on top of the JBindery icon.

If you now get:

Congratulations! Your program works.

top

3. Creating Your First Applet

HelloWorldApp is an example of a Java application, a standalone program. Now you will create a Java applet called HelloWorld, which also displays the greeting "Hello world!". Unlike HelloWorldApp, however, the applet runs in a Java-enabled Web browser such as HotJava, Netscape Navigator, or Microsoft Internet Explorer.

To create this applet, you'll perform the basic steps as before: create a Java source file; compile the source file; and run the program.

a. Create a Java Source File.

Again, you have two options:

  • You can save the files HelloWorld.java(in a .java source file) and Hello.html(in a .java source file) on your computer and avoid a lot of typing. Then, you can go straight to step b.

  • Or, you can follow these instructions:

1. Start SimpleText. Type the following code into a new document: 

import java.applet.*;
import java.awt.*;
 
/**
 * The HelloWorld class implements an applet that
 * simply displays "Hello World!".
 */
public class HelloWorld extends Applet {
    public void paint(Graphics g) {
        // Display "Hello World!"
        g.drawString("Hello world!", 50, 25);
    }
}

Save this code to a file called HelloWorld.java.

2. You also need an HTML file to accompany your applet. Type the following code into a new SimpleText document:

<HTML>
<HEAD>
<TITLE>A Simple Program</TITLE>
</HEAD>
<BODY>
Here is the output of my program:
<APPLET CODE="HelloWorld.class" WIDTH=150 HEIGHT=25>
</APPLET>
</BODY>
</HTML>

Save this code to a file called Hello.html.

Make sure that your files HelloWorld.java and Hello.html are in the same folder.

b. Compile the Source File.

Compile the HelloWorld.java source file using javac.

The compiler should generate a Java bytecode file, HelloWorld.class.

c. Run the Program.

Although you can view your applets using a Web browser, you may find it easier to test your applets using the simple Applet Runner application that comes with the JavaTM Platform. To view the HelloWorld applet using Applet Runner, Open the folder Apple applet viewer in the MRJ SDK 2.1 folder. There should be an application called Apple Applet Runner.

Drag and drop your Hello.html file on this application.

Now you should see:

Congratulations! Your applet works.

top

4. Where to Go from Here

To continue your introduction to the Java programming language, check out these trails:

  Getting Started(in the Getting Started trail)
  Learning the Java Language(in the Getting Started trail)

top

About the Author

Werner van Mook transformed the original Win32 Cup of Java to this Macintosh version.
Werner is an employee of Syntegra based in The Netherlands and a soon-to-be Certified Java Developer.
After seven years of delivering Macintosh support he switched to the windows platform and got his MCSE+I in eleven months. Since December 1998 he is a B. of Sc. in informatics.

Previous Page Lesson Contents Next Page Start of Tutorial > Start of Trail > Start of Lesson Search
Feedback Form