Java Programming Language

Have you ever wondered how computer programs work? Have you ever wanted to learn how to write your own computer programs? Whether you are 14 years old and hoping to learn how to write your first game, or you are 70 years old and have been curious about computer programming for 20 years, this article is for you.

Here are several vocabulary terms that will make things understandable:

• Computer program - A computer program is a set of instructions that tell a computer exactly what to do. The instructions might tell the computer to add up a set of numbers, or compare two numbers and make a decision based on the result, or whatever. But a computer program is simply a set of instructions for the computer, like a recipe is a set of instructions for a cook or musical notes are a set of instructions for a musician. The computer follows your instructions exactly and in the process does something useful -- like balancing a checkbook or displaying a game on the screen or implementing a word processor.

• Programming language - In order for a computer to recognize the instructions you give it, those instructions need to be written in a language the computer understands -- a programming language. There are many computer programming languages -- Fortran, Cobol, Basic, Pascal, C, C++, Java, Perl -- just like there are many spoken languages. They all express approximately the same concepts in different ways.

• Compiler - A compiler translates a computer program written in a human-readable computer language (like Java) into a form that a computer can execute. You have probably seen EXE files on your computer. These EXE files are the output of compilers. They contain executables -- machine-readable programs translated from human-readable programs.

In order for you to start writing computer programs in a programming language called Java, you need a compiler for the Java language. The next section guides you through the process of downloading and installing a compiler. Once you have a compiler, we can get started. This process is going to take several hours, much of that time being download time for several large files. You are also going to need about 40 megabytes of free disk space (make sure you have the space available before you get started).


Downloading the Java Compiler

In order to get a Java development environment set up on your machine -- you "develop" (write) computer programs using a "development environment" -- you will have to complete the following steps:

1. Download a large file containing the Java development environment (the compiler and other tools).
2. Download a large file containing the Java documentation.
3. If you do not already have WinZip (or an equivalent) on your machine, you will need to download a large file containing WinZip and install it.
4. Install the Java development environment.
5. Install the documentation.
6. Adjust several environment variables.
7. Test everything out.
   

Before getting started, it would make things easier if you create a new directory in your temp directory to hold the files we are about to download. We will call this the download directory.

Step 1 - Download the Java development environment

Go to the page http://java.sun.com/j2se/1.4.2/download.html. Download the SDK software by clicking on the "Download J2SE SDK" link. You will be shown a licensing agreement. Click Accept. Select your operating system and download the file to your download directory. This is a huge file, and it will take several hours to download over a normal phone-line modem. The next two files are also large.

Step 2 - Download the Java documentation

Download the documentation by selecting your operating system and clicking the SDK 1.4.1 documentation link.

Step 3 - Download and install WinZip

If you do not have a version of WinZip or an equivalent on your machine, go to the page http://www.winzip.com/ and download an evaluation copy of WinZip. Run the EXE you get to install it. We will use it in a moment to install the documentation.

Step 4 - Install the development kit

Run the j2sdk-1_4_1-*.exe file that you downloaded in step 1. It will unpack and install the development kit automatically.

Step 5 - Install the documentation

Read the installation instructions for the documentation. They will instruct you to move the documentation file to same directory as that containing the development kit you just installed. Unzip the documentation and it will drop into the proper place.

Step 6 - Adjust your environment

As instructed on this page, you need to change your path variable. This is most easily done by opening an MS-DOS prompt and typing PATH to see what the path is set to currently. Then open autoexec.bat in Notepad and make the changes to PATH specified in the instructions.

Step 7 - Test

Now you should be able to open another MS-DOS window and type javac. If everything is set up properly, then you should see a two-line blob of text come out that tells you how to use javac. That means you are ready to go. If you see the message "Bad Command or File Name" it means you are not ready to go. Figure out what you did wrong by rereading the installation instructions. Make sure the PATH is set properly and working. Go back and reread the Programmer's Creed above and be persistent until the problem is resolved.

You are now the proud owner of a machine that can compile Java programs. You are ready to start writing software!

By the way, one of the things you just unpacked is a demo directory full of neat examples. All of the examples are ready to run, so you might want to find the directory and play with some of the samples. Many of them make sounds, so be sure to turn on your speakers. To run the examples, find pages with names like example1.html and load them into your usual Web browser.