Friday, February 23, 2018

Introduction to Java Programming

Hello again. Welcome back to another one of our hopefully really good articles on Java programming. If you’re reading this, then I’m assuming you read the last post on installing java software (if you haven’t, you can do so by clicking the link here). If you have read the last post, then by now you should have successfully installed the Java Runtime Environment, the Java Development Kit and the NetBeans IDE software.
(N.B.: The majority of these tutorials will be done using NetBeans, but those using other IDEs like Eclipse are also free to follow through).
This week, we’re going to take a quick look at the NetBeans environment, explain how coding in Java works, and at the end, we’ll run our first piece of code.
So let’s start learning.

Before go ahead see the last articles 
  1. Making Games With Java- Introduction
  2. Getting Everything you need for Java


I want to believe that all those reading this have successfully downloaded and installed everything we mention in the last post. If you want to make sure that the JRE has been installed, or you want to know the directory that it is saved into (I don’t know, maybe you’re just curious), what you can probably do is access the JAVA_HOME environment variable.
In case this is new to you, an environment variable is a string variable (we’ll talk about string variables in a later post) that stores information like the drive, path or name of a particular file. Now, what the JAVA_HOME variable does is point to the directory where your JRE is saved.
To access this, all you have to do is open the Control Panel, access your system settings, and look for “Advanced System Settings”. This should open the following dialog box:

Click on “Environment Variables”, and you should see the JAVA_HOME variable in the new dialog box, under the “System Variables” tab. In fact, if you double-click it, you will see a dialog box that will allow you to change the variable name and directory.
Now let’s move on.

How Java Coding Works

Traditionally, java code (and all code for that matter) is written using a text editor (NetBeans, and most IDEs, comes with a special area for writing code. The source code (or code written by you) is saved with the extension “.java”, and the compiler (a program known as Javac) then converts the source code into machine code (1s and 0s), in a process known as Compiling.
When the compiling process is over, and if there are no errors, Javac creates a new file with a “.class” extension, which is then run by the Java Virtual Machine.
NetBeans takes care of all of this for you, creating the files, compiling the source code, and running these programs in its own software, thereby saving you the trouble of writing long strings of code in a console window. (Aren’t IDEs great?)
Now that you know the basics of coding, time to start your engines! (By that, I mean run the NetBeans, or whatever it is you’re using).

When you launch the software, it should look something like this:

It’ll take a little while to load though, so maybe you can play a quick game of Minesweepers while you wait. Or, I don’t know…

To open the coding window, go to “File > New Project” or click the keyboard shortcut “Ctrl-Shift-N”. You could also look under the toolbar for this symbol
. Whatever you do, you’ll see this dialog box.

Since we’ll be making a Java application, select “Java” under Categories, then under Projects, select “Java Application”, like was mentioned before. You’ll then see this dialog box:

Yeah, I know; so many dialog boxes, right! Don’t worry, this is the last one. Type in the project name in, well, the Project Name text box (it’s actually quite self-explanatory). Let the name be TutorialProject (with no space). You’ll notice what happens in the text area next to the “Create Main Class” checkbox (make sure this is checked by the way; I’ll explain why later). As you write “TutorialProject” in the Project Name text box, the same will appear in the second text box, but this time with lowercase. In simple terms, it will generate something like this:


The “TutorialProject” with upper case is the name of the class file created by the IDE, while the one in lower case is the name of the package it is contained in. You can set the default location of your java project in “Project Location” or you can leave it at the default (NetBeans will create a folder with the projects name) and when you’re satisfied, click “Finish”.

You should almost instantly be taken to the coding window, which should look a lot like this:

Now, if you would please direct your attention to the left of this, you should notice this window:

Your “Project” window would most likely be mostly empty (save for the TutorialProject) since the software is newly installed. Click the plus by the little coffee mug and you’ll see this:
Click the plus by the Source Packages, and you’ll see the package name (which is the same as your project name). Expand that and you’ll see the java source file:
But enough of all the software stuff, let’s take a look at some java code.

A Look at some code

Now when you look at the coding window, you’ll probably notice some lines of code written there. You’ll see some words in blue, some in black and some that are greyed out, and you seem kind of overwhelmed. It’s kind of like standing in a glass museum; everything looks beautiful and new, but you’re afraid to touch anything, because doing so might wreck the entire thing.
Don’t get me wrong, this is quite true. But don’t worry, that’s why I’m here. To walk you through this complicated minefield we call Java.
Now first off all…


…you’ll probably notice some words that are greyed out in the code. You also notice that they have a lot of slashes and asterisks in them, and at first, they probably look like some sort of cool, complicated code that you shouldn’t mess around with.
But don’t be scared, these greyed out lines are called comments, and they’re relatively useless. In fact, I could delete all of them right now, like so:

Ta da! No consequences! And the code looks a lot less complicated too!
Now, I’m sure you’re wondering right now “Wait, if those things aren’t. Say, you just wrote this mad 300-line code for, like, a game or something, and then feeling proud of yourself, you close your system and go to sleep. The next day, you want to show it off to your fellow coding buddy, and he (also impressed) asks you what something does. You open your mouth, about to tell him what is obviously painstakingly obvious…
But you can’t tell him anything. You code is long and complex, you can’t remember what anything does. And now, you can’t tweak it, because you’re too afraid to touch it, because you have no idea what anything does.
Sad, but true.
Now, you can prevent this with comments. These greyed out lines are very useful in describing what each part of the code is used for. The best thing is, the compiler completely ignores them when run, so you can write anything you want. I prefer to delete the comments that NetBeans generates, but you can leave them if you want.
To create a comment, simply start whatever you want with two forward slashes, e.g.:
//This is a comment
But this will only last for one line. If you want to comment out more than one line, you could do this:
//This is a comment
//This is another comment
Or, even simpler and more efficient, start the line you wish to comment with a forward slash and two asterisks, and end it with an asterisk and forward slash, i.e.:
/** This is a
Multiline comment


If you removed the comments, the first thing you would see is this line:
package tutorialproject;
This is just the name of the java package you created. Note the semicolon at the end. It’s quite necessary to end all lines of code with a semicolon, or else it won’t work. Also, it’s not compulsory for the package name to be the same as the project name, or class name. If you had renamed it while creating the project earlier, it wouldn’t really matter.
The next thing would be:
public class TutorialProject {
This is the name of the class file created while compiling. You can think of it as the area where code is written, with the curly brackets ({}) defining the borders of this area. Any code run outside these curly brackets will not be run with the remaining code, and will most likely generate an error message.
Looking in the curly brackets now, you’ll see this:
  public static void main (String[ ] args ) {
And it comes with its own curly brackets too (the same conditions apply). This is called the main method (hence the name “main”). Never mind what a method is now; we’ll talk about that in a later post. Just think of it now as a chunk of code, and the main method is the chunk of the code that the compiler runs first. You’ll likely receive error messages if there is no main method, and for now, this is where you’ll input most of your code.
(Don’t worry about all those words like “static” and “public” and those stuff in the bracket, we’ll explain those when we explain methods).
Now before we round off, it’s only fair that we run at least one code.


What we’re going to do is print out something to the console window. Quick, add this in between the curly brackets of your main method:
System.out.println(“Hello World”);
When you type in System and put the dot, this happens:

Double click the “out” option and type a dot; the this will happen:

Double click “println” and a bracket will also appear with the statement. In the bracket, put quotation marks and type “Hello World”, then outside the brackets, put a semicolon (always remember the semicolon. It will save you a lot of sleepless nights as you advance as a programmer).
At the end, your code should look like this:


Okay, so what this is going to do is print out “Hello World” into the system console. The word “System” is the keyword which calls the console out. The keyword “out”, well, think of it as short for output. And “println”, obviously enough, is the keyword which tells the system to print whatever you want. (Keep in mind, “ln” is small letter ‘L’ and n, not capital letter ‘I’ and ‘n’).

After the println, there’s a bracket, with “Hello World” in quotation marks. It is very important to put it in quotes, because if not, the computer will mistake the output for code, and there will be an error. Watch what happens when I remove the quotes:

You notice that red line? Yeah, that means there’s an error.
In short, you’re saying “Computer, print out whatever I put in that bracket, which is “Hello World”. You can put anything you want in the quotes. It will print out!
Now let’s run this thing. There’s a number of ways to do so. One is to right click on the window and click “Run File” from the pop-up window that pops up. Another way is to click this symbol on the toolbar, or you could go to the Run menu and click Run. Or, if you prefer keyboard shortcuts, click F6 or Shift-F6.
Either way, when you run it, you’ll notice some processes taking place, and this will pop-up with your message:

If you see this, then congrats! You’ve just run your first successful java code.

See you next post, where we’ll most likely be discussing variables and data structure.

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Thanks for Reading 


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