Building Your First Java Program: Starting From Scratch

Welcome to CS 1331! If this is your first time using a corporate-grade programming language, then you will probably find this tutorial quite useful! The point of this guide is to familiarize you with the basic workings of Java enough to allow you to install and configure the Java Virtual Machine, set up any path settings, and setup an Integrated Development Environment (IDE) to then write the actual Java code. Hopefully, this will give you enough knowledge and elbow room to experiment and learn more about Java on your own. Good luck!

This part will cover installation of the newest version of Java, 5.0, on your computer. First, however, you must check to be sure that you have no previous version of Java installed and, if you do, you must uninstall it before continuing. So first we will check for previous installations. (Note that the previous version of Java was 1.4.x, and this one would equivalently be 1.5.0, but Sun is simply calling it Java 5.0.)

Let's begin by opening up your Control Panel. Double click on "My Computer", and from the menu along the left panel of the window, select "Control Panel."

Important! Once the Control Panel comes up, check the left panel again. If there is an option there called "Switch to Classic View," select it now. Otherwise, if it says "Switch to Category View," leave it alone.

Now, select the "Add or Remove Programs" icon from the list - it should be one of the first couple ones across the top. From the list of programs that then pop up, scroll downward and look for any program(s) with the name "J2SE" in it. If you find one or more, note the version number. If the version number is different than 5.0 (a common previous one is 1.4.2), you will need to uninstall those Java programs before continuing. You can do this by selecting the programs and clicking the "Change/Remove" button that appears and following the directions. If the version number is 5.0, then you can skip the rest of this installation chapter, as you have the newest version of Java running! If there is no J2SE installation listed, or you have already uninstalled a previous installation, simply keep reading!

The next step will be to download Java itself! You have a few options on where to locate a working copy of Java. The first option is off the CD that comes with your Lewis & Loftus Java book. Installing it is simple enough--follow the instructions for the installer and you should be good to go. Note, however, that Java is not actually on the CD. Rather, it will come from the internet, so make sure that your computer has a network connection when you pop in the CD.

Your second option is to download Java off the Internet manually. To do so, direct your favorite web browser to http://java.sun.com. Here, at Sun's Java home page, you will find anything and everything on the Java programming language. Most of what you'll find here, such as developer news and JVM specifications, you probably won't have much interest in. However, what you are looking for is the Java Runtime Environment, essentially the Virtual Machine, which will drive your Java applications.

A more direct link to the available Java software is: http://java.sun.com/j2se/1.5.0/download.jsp

From here you will find the following available:

J2SE 5.0 JRE
This is the Java runtime environment, which allows you to run Java applications on your computer. It does not allow for the creation of Java programs so it is not sufficient for our purposes, but using it allows a person to view Java applets in websites and run any other programs which utilize the Java VM.

J2SE 5.0 JDK
This is the Java Software Development Kit. This is what you'll need for this course, and is what this tutorial follows. It includes the Java Runtime Environment as well as provides the tools necessary for creating your own Java applications. However, to make application creation even easier for you, there will be one more tool that we will need to track down...

At this point, select the J2SE 5.0 JDK option for download. Read through the license agreement, click "Accept"

Now you will be at the download page. Here, you will have a few choices of the computer types to choose from. As a Windows user, you will have a choice of downloading and installing Java directly off the Internet, or downloading the installer itself and installing Java without needing an Internet connection. The full online installation uses much less hard drive space, but the choice is up to you. Both should be nearly identical in process.

Save the file in a place that you will remember, sit back, and wait!

Once the download is complete, you should navigate through your file system to whatever folder you actually downloaded the Java SDK installer into and double-click on the file. You'll pretty much just follow on the onscreen instructions, and you can also most likely leave all the values at their defaults. However, at some point it may ask you about multiple language support (which is up to you) as well as web browser support. Whatever web browser you use, make sure you check its box, as this will allow that browser to view applets.

Congratulations! You've installed Java. Now to configure it!

If you are running Tiger (Mac OS X 10.4.2), Java 5.0 is now available for download. Go to (http://www.apple.com/support/downloads/java2se50release1.html) and download and install the Java 5.0 package. After installing Java 5.0, you need to set this version as the default version. To this end, double click on your Macintosh HD icon. From the window that pops up, scroll down and find the folder titled "Applications" and then, within this folder, folder "Utilities." Open up this folder and navigate through it until you find the program called "Terminal." Fire up the terminal, and at the prompt, type:

open -a /Applications/Utilities/Java/J2SE\ 5.0/Java\ Preferences.app

If you are running a previous version of Mac OS X (i.e., version 10.4.1 or earlier), Java 5.0 is not available for your platform. In this case, we strongly suggest that you upgrade to Tiger and install Java 1.5, to avoid problems. If you decide not to install Tiger, we provide instructions on how to modify your Java library to add to it a version of Java 1.5's Scanner class. Although using such modified library should allow you to do homeworks that would otherwise require Java 5.0, the provided Scanner class has limited functionality, and we cannot exclude that it may behave incorrectly in some cases. If you still decide to go for this solution, follow the instructions at http://www.cc.gatech.edu/classes/AY2006/cs1322_fall/macscanner.html.

Now that Java is installed, we will configure it!

Now we need to set up the path environment variables so you can compile and run your programs from the command line.

Want to do all of this automatically?
Then run this program to automatically configure your paths for the JVM, and none of the other steps for this section are required!

This section isn't so much about configuring the VM itself, as it is setting up Windows to recognize exactly where the VM is. In order to this, you must once again access the Control Panel:

Again, if the next window that comes up says "Pick a Category" across the top, click the "Switch to Classic View" option to the right of it.

Now, click on the "System" icon. This should bring up a tabbed "System Properties" window.  Click on the "Advanced" tab.

Near the bottom of the window will be a button with the title "Environment Variables"

From the list of variables on the bottom, highlight the one that says "PATH"

Click the "Edit" button, then in the "Variable Value" field, put a semicolon ( ; ) at the end of whatever is already there, and then type the following:

C:\Program Files\Java\jdk1.5.0\bin

(Note: if you installed the latest JDK from Sun's website, the path will NOT be the same as above.  In this situation, please use the automated program listed above to set up your environment variables)

Click ok, reboot your computer, and your system should be able to find the Java VM!

If you followed the instruction for Java 5.0 installation given above, your Java should be already configured correctly. If you plan to use Java from the command line, though, make sure to add to your command path, as the first entry, the following path:

/System/Library/Frameworks/JavaVM.framework/Versions/1.5/Commands

As mentioned earlier, IDE is short for Integrated Development Environment. Essentially, this means it's a nice and pretty and easy-to-use interface in order to write all your code and subsequently run, test, and debug your programs. You could, technically, develop all your code without an IDE. However, an IDE can greatly simplify many tasks, and for the purposes of this class, making it that hard on yourself won't help you in the least. Here is a quick summary of the more well-known IDEs out there.

An important note to remember: If you have never used an IDE before (examples listed in bold below), we strongly recommend using the IDE provided on the CD you can find in your book: JGrasp. Find its description in the list of IDEs below for information on where to find JGrasp if you do not have a copy of the CD in the book. Note that almost all the other IDEs have some quirks which make them tricky to use on our HW assignments, unless you really know what you are doing. Use them at your own risk!

JGrasp
JGrasp is a relatively simple IDE to use and has been designed to help out new java programmers. It comes with a built-in debugger, which you may find valuable a little later in the course. This will be the IDE this tutorial focuses on. This is also the IDE that CS 1331 officially supports. It can be found for download on the JGrasp website, but you can also install it directly off the CD that comes with your Java book. If you are a CS major, you might want to look into an IDE with a little more power, at least for future use. For the purposes of this class, this IDE and any others listed here will do just fine.

JCreator
This is a favorite for most middle-of-the-road programmers. It is quite easy to use, has a very friendly interface, and has a free version that can be downloaded off the internet from the JCreator webpage. This IDE will satisfy the majority of programmers out there, from the beginners all the way up to most recreational programmers ("Wait, you mean people program for fun?..."). For most upper-end and corporate developers, however, it becomes relatively underpowered.

NetBeans
This is the IDE which Sun offers in one of its downloads, packaged with the Java Software Development Kit. It is a significant step above JGrasp in terms of both learning curve and programming power, and also sports a graphical GUI builder, which can make GUI assignments much easier to accomplish. You can download NetBeans either from the Sun website, or from the NetBeans website.

JBuilder
This IDE is along the same lines as NetBeans and is also available on numerous platforms. It boasts syntax-correcting help functions, easy plug-in capabilities with 3rd party Java packages, and some powerful project management capabilities. For the average programmer, this may be more than is needed, plus its learning curve is a tad steep. However, this will satisfy most high-end and corporate programmers. JBuilder can be downloaded off the JBuilder website. You may need to register to download JBuilder.

Eclipse
Probably the favorite among hardcore CS majors at Georgia Tech (ask any CS 2335 student), Eclipse is the ultimate in both power and configurability, sporting syntax and coding style correction plug-ins, graphical GUI editors, automatic code and javadoc completion functions, and dozens more with its extensive plug-in library. Its only downside is its learning curve, and its programming power far exceeds what you will need for this course. However, if you plan on taking more CS courses down the road, it is something you may at least want to have a look at eventually. It is available for free download off the Eclipse website.

As an interesting side note, it is worth mentioning that it is entirely possible to write your Java files in plain text editors like Windows Notepad. Additionally, if you are of the more ambitious type, famed text editors like Emacs or vi (in which this help file was written!) can be used as well to generate your source code. In fact, many students prefer actually typing in code initially through some text editor such as Notepad, emacs, or vi and then opening that file in JGrasp. (But make sure not to use Word!) Once your source text file has been opened in an IDE, it can be edited in whatever ways you wish, compiled, and run.

Alright! You're in the home stretch for setting up Java and getting your first application off the ground. Bear with me for just a little longer - you're already well beyond the hardest parts (unless I screwed up somewhere and something isn't working quite right, in which case you should contact your TA or instructor!).

From the "File" menu, create a New Java file. This should instantly create a new text file in the large blank space of your JGrasp window. Type these mysterious words into this text window:

public class Test {

  public static void main(String [] args) {
    System.out.println("Hello!");
  }

}             

My my, this sure looks mysterious! Let's see what this code means, exactly. The first part:

This is a declaration. It is creating a class called "Test." A class, in Java, is more accurately known as an Object. Think about Object intuitively, as you would any actual tangible, physical object that does...something. A car, for instance, could be an Object. All Object have attributes, or the specific aspects of the Object that make it what it is. For a car, its attributes could be tires, seats, power locks, XM radio, a turbocharged V6, a 6-disc changer...you get the idea. Objects will also have member methods, or the functions that cause the Object's attributes to interact together, or even with other Objects, to accomplish certain tasks. For instance, with the assistance of roads and signals, and utilizing its power steering, tires, and engine, a car can "drive."

For this example, we're keeping it simple. This class, or Object, will not do anything other than print out some sentences.

An important thing to note, first. Java is picky about syntax. Whatever you name the .java file (the file in which you will write your programs), that must also be the name of the class itself (the word after "public class ____"), and it is case-sensitive.

Now back to our original text window. You should have typed in the original example, and now you should save it. Go to "File" and select "Save As." Type in "Test.java" and save wherever you feel appropriate (as a good rule of thumb, save all your .java files for a single project in the same folder). Now, your window should look something like this:

Now that you have the class name and file name matching correct, let's continue with our analysis of this short block of code. The next part:

Without going into too much detail about the meanings of each individual word there, just know that every project you write will need to have at least one of these in it. When you run the project, this is what Java will look for at the very beginning, and execution of your entire project will start here. Next line:

Here, an Object is being used! It is an Object called "System," and we are using one of its member methods to do something. In this case, the method is called "println" and it prints out to your monitor whatever is written inside the quotation marks that are inside the parenthesis.

Remember, Java is very picky about syntax, so every curly brace you open, you must close. Every opening parenthesis must be matched by a closing parenthesis. Also, you need semicolons at the end of every line of execution code (as shown in the example).

Now the moment of truth! Let's see if this sucker runs and does what it should. From the "Compiler" menu, choose "Compile." The rectangle at the very bottom of the screen should now be displaying some bizarre commands as the Java compiler and Virtual Machine go to work. Should everything behave properly, you should eventually see a "process completed" output appear, signaling that compilation went fine and your Object is now ready for execution. From the "Run" menu, select "Run," and you should see everything inside the println( ) parenthesis print out into the rectangle! Experiment and change what is inside those parenthesis, recompile the file, and run it again.

Interestingly enough, there are no differences between writing a class / Object in Windows as opposed to Macintosh, as both use the same JGrasp IDE to do so. The only difference comes in at the command line compilation and execution. For the purposes of easy reading, all pertinant information about writing a class, compiling it, and running it in JGrasp will be copied here.

Alright! You're in the home stretch for setting up Java and getting your first application off the ground. Bear with me for just a little longer - you're already well beyond the hardest parts (unless I screwed up somewhere and something isn't working quite right, in which case you should contact your TA or instructor!).

From the "File" menu, create a New Java file. This should instantly create a new text file in the large blank space of your JGrasp window. Type these mysterious words into this text window:

public class Test {

  public static void main(String [] args) {
    System.out.println("Hello!");
  }
}

My my, this sure looks mysterious! Let's see what this code means, exactly. The first part:

This is a declaration. It is creating a class called "Test." A class, in Java, is more accurately known as an Object. Think about Object intuitively, as you would any actual tangible, physical object that does...something. A car, for instance, could be an Object. All Object have attributes, or the specific aspects of the Object that make it what it is. For a car, its attributes could be tires, seats, power locks, XM radio, a turbocharged V6, a 6-disc changer...you get the idea. Objects will also have member methods, or the functions that cause the Object's attributes to interact together, or even with other Objects, to accomplish certain tasks. For instance, with the assistance of roads and signals, and utilizing its power steering, tires, and engine, a car can "drive."

For this example, we're keeping it simple. This class, or Object, will not do anything other than print out some sentences.

An important thing to note, first. Java is picky about syntax. Whatever you name the .java file (the file in which you will write your programs), that must also be the name of the class itself (the word after "public class ____"), and it is case-sensitive.

Now back to our original text window. You should have typed in the original example, and now you should save it. Go to "File" and select "Save As." Type in "Test.java" and save wherever you feel appropriate (as a good rule of thumb, save all your .java files for a single project in the same folder). Now, your window should look something like this:

Now that you have the class name and file name matching correct, let's continue with our analysis of this short block of code. The next part:

Without going into too much detail about the meanings of each individual word there, just know that every project you write will need to have at least one of these in it. When you run the project, this is what Java will look for at the very beginning, and execution of your entire project will start here. Next line:

Here, an Object is being used! It is an Object called "System," and we are using one of its member methods to do something. In this case, the method is called "println" and it prints out to your monitor whatever is written inside the quotation marks that are inside the parenthesis.

Remember, Java is very picky about syntax, so every curly brace you open, you must close. Every opening paren must be matched by a closing paren. Also, you need semicolons at the end of every line of execution code (as shown in the example).

Now the moment of truth! Let's see if this sucker runs and does what it should. From the "Compiler" menu, choose "Compile." The rectangle at the very bottom of the screen should now be displaying some bizarre commands as the Java compiler and Virtual Machine go to work. Should everything behave properly, you should eventually see a "process completed" output appear, signaling that compilation went fine and your Object is now ready for execution. From the "Run" menu, select "Run," and you should see everything inside the println( ) parenthesis print out into the rectangle! Experiment and change what is inside those parenthesis, recompile the file, and run it again.

Compiling and Running Java programs from the command prompt

It is important to know how to compile and run your code from the command line, as this is how the TA's will be grading all of your work.  Before submitting your homework, it is highly recommended that you verify that your code compiles and runs from the command line.

Using Windows:

To open up a command prompt, click the your "Start" button, and then click "Run."  Type "cmd" and hit Enter, and a new window should pop up that is black and has some gray depressing text on it. You will need to navigate to the directory where you saved your .java files.

Type the command as you see it there, except replace everything after the backslash ( \ ) with the path to wherever you saved your .java files.

To compile the files, enter:

javac JavaClassNameHere.java

Where "JavaClassNameHere" is the name if your Java program.  If you want to compile all the files in the current directory, enter:

javac *.java

To then run the compiled code, enter:

java -cp . JavaClassNameHere

(for the example Test.java class specified above, the command to run would be "java -cp . Test")

The "-cp ." parameter specifies the "class path", which is the directory that any required class files are read from
(If your confused about what this means, don't worry, as its not important to understand right now.  But just remember to use the javac command as specified above.)

Notice that you must specify the .java extension when you compile, but not when you run the code.

Using a Mac:

The procedure for compiling and executing java code from a command prompt is the same for all operating systems, in that the syntax for using java and javac are identical for Windows, Mac, and Unix (Linux) systems.

Refer to the Compiling and running under windows above, only use the "terminal" or "shell" to access a command prompt

Congratulations! You have successfully learned about, downloaded, installed, and configured the Java Virtual Machine and software development kit, as well as tied a fully-functional IDE in with it to ultimately produce a working Java application! Not to mention, you can now look like an erudite programming guru by compiling and running your source files from the command prompt.

This tutorial was meant to give some insight into getting an introductory Java course off the ground, especially to those have had little or no previous programming experience. I have almost always found the most difficult part of the course not to be the homeworks or exams or quizzes, but rather setting up everything that I need to complete all those assignments, and unfortunately, it is this "setting up" information that seems the hardest to come by. To those in the same boat as I, this is for you. Remember that there are also countless other useful IDEs out there aside from the ones mentioned here.

I hope you have found this introduction to be useful. As you become more comfortable in the Java programming environment, you will find most IDEs to be friendly in terms of their flexibility with your goals for your programs. As a disclaimer, if you are having ANY problems doing anything mentioned in this tutorial, do not be hesitant to ask any of your TAs, professors, or even fellow students for clarification, as getting all this basic functionality to work is crucial to successfully completing CS 1331. Even a week of dealing with dysfunctional classpaths and sick Virtual Machines can set your integration into CS 1331 back several weeks.

Good luck and good programming!