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, 9.0, on your computer. It is important that you have this new version on your computer. To begin, you may want to check to be sure that you have no previous (8 or earlier) version of Java installed and, if you do, you must uninstall it before continuing. So first we will check for previous installations.

Let's begin by opening up your Control Panel. Go to the Windows search panel in the bottom left and start typing "control panel". (see below) Then select the Control Panel from the menu of choices that come up.

Now, select the option "Programs - Uninstall a Program" from the list. From the list of programs that then pop up, scroll downward and look for any program(s) with the name "Java SE Development Kit" in it. If you find one or more, note the version number. If the version number is 8 or less, you may want to uninstall those Java programs before continuing (though it is not required). You can do this by selecting the programs and clicking the "Uninstall" item that appears at the top. If the version number is 9, then you can skip the rest of this installation chapter, as you have a new enough version of Java running for our class! (As of this writing, java is at Update 1 of version 9, so if you have an earlier Update, you still may want to install the newest one.) If there is no Java installation listed, or you have already uninstalled a previous installation, simply keep reading!

The next step will be to download Java itself! Go to the Java download page at http://www.oracle.com/technetwork/java/javase/downloads/index.html and look for the "JDK 9" option. Click "Download JDK". This may take you to a second page. You want to look for the most recent Java SE. Choose your platform and language, read through the license agreement and click "Continue". (If you are on a newer Windows machine, you likely want the Windowsx64 version.) Be sure you are downloading the JDK and not "JRE".

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!

Follow the steps below to set up Java on your Mac.

1. Visit Oracle's java download site and select the JDK Download option.
2. Download the macOS option
3. Open up the downloaded .dmg file and follow the instructions
4. Open up the Terminal (either from the Applications folder or Spotlight search)
5. Type "java -version", hit enter, and verify the output at least says java version "9.0.1"
6. Type "javac -version", hit enter, and verify the output at least says javac 9.0.xx (xx is some number)

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.

This section isn't so much about configuring the VM itself, as it is setting up Windows to recognize exactly where the VM is. First, locate the Java installation on your computer. Open an Explorer window, then (assuming you installed it in the default location) navigate to C:\Program Files\Java. You should see one more more folders; find the one starting with "jdk" with the highest number (it's possibly jdk-9.0.1).

Note that if you only have folders here starting with "jre", then you have only installed the Java Runtime Environment on your machine. That is not good enough for our class. So in that case, go back up higher on this page and follow the instructions for downloading the "jdk".

OK, assuming you have the jdk on your machine, open that folder, then find the bin folder inside. Open the bin folder and look for a program called "javac.exe". If you see the program, you've found the correct folder. The full path should be something similar to C:\Program Files\Java\jdk-9.0.1\bin. Copy your path to your clipboard or memorize it. Now, you must once again access the Control Panel:

Follow the directions earlier on this page in the "Java Installation Overview" section to access the Windows Control Panel, which will give you the window below. Click on the "System and Security" item in the dialog box.

Now, click on the "System" item.

This should bring up a window with lots of information about your computer. Click on the "Advanced system settings" item over on the left side.

This should bring up a "System Properties" window. Near the bottom of the window will be a button with the title "Environment Variables". Click on that.

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

This will bring up a list of all the different folders in which Windows will look for executable programs on your machine. You want to find one that has the jdk in it, something like C:\Program Files\Java\jdk-9.0.1\bin. This is the one that refers to your folder holding all the java executables in it. Make sure that the update number, e.g., 01 here, matches the update of java that you have on your computer. If no such jdk folder exists in the list of folders being shown in this dialgo box, then you need to add it. Note: The very first folder listed in this dialog might be a folder called something like C:\ProgramData\Oracle\Java\javapath. This is a shortcut that Oracle adds on. If this does appear, select that folder and delete it from the list. It will not be good enough for you to run all the java programs we need.

Click ok, close any command prompts you might have open, and your system should be able to find the Java VM after you open a new command prompt. You can test by opening a command prompt and typing "javac"...if it says "not recognized as an internal or external command", it isn't working yet. If it doesn't work immediately, be sure all command prompts are closed and try again. If that doesn't work, then you likely made a mistake somewhere along the way, and we recommend getting some help from a TA who can assist you to get it set up properly.

If you have Java 9 on your machine, it is likely configured correctly to be used. If you aren't able to run java from the command line, you likely need to add /usr/bin to your path. Consult the documentation for your command shell in case you do not know how to modify your command path.

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 JGrasp. Find its description in the list of IDEs below for information on where to find JGrasp. 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 with Prof. Stasko officially supports. It can be found for download on the JGrasp website. 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.

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.

NetBeans
This is another popular IDE for Java. 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 Oracle website, or from the NetBeans 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 Sublime Text (highly recommended), Atom, or Notepad++. Additionally, if you are of the more ambitious type, famed text editors like Emacs (Prof. Stasko's favorite -- what a dinosaur!) or vi can be used as well to generate your source code. In fact, many students prefer actually typing in code initially through some text editor 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. To learn more about the command line in general and to get some tips for using the Windows command prompt, see Command Line Crash Course.

Using Windows:

To open up a command prompt, go to the Windows search box in the lower left of your computer's interface and start typing command prompt. Choose the "command prompt" program. 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 (folder) where you saved your .java files. To do this, use the "cd" command, which stands for "change directory". An example of doing this is shown below.

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!