Unit 1: Introduction to Java

What is programming?
What is Java?
Your First Java Program

What is programming?

Programming is basically the act of writing instructions for a computer. The good news is that a computer will do exactly what you tell it to do. The bad new is… a computer will do exactly what you tell it to do.

This means that to be a successful programmer, you will not only need to know the syntax (rules) of a programming language (such as Java), you will also need to be detail-oriented when using those rules.

What is Java?

Java is an object-oriented programming language (OOP). That categorization will make more sense when you learn more about objects in Unit 5.

Java is also a compiled language, which means that once you write the source code it goes through a compiler before running in order to convert the code into bytecode, which machines can understand. This is nice because a lot of errors can be caught during compile, which prevents things from going wrong if you were to just run the code right away.

The reason why we’re teaching it here is because most FTC teams use Java to program their robots. Java is also a widely popular language for a variety of reasons we’re not going to get into here.

If you want to learn more about Java, here’s its Wikipedia article.

Your First Java Program

It’s time to fire up your IDE or editor and start coding!

To preface this exercise, we will explain everything later. For now, just type what you see exactly as you see it. (We also recommend not copying and pasting example code because that kinda defeats the point of learning how to code.)

Open your IDE or editor. From now on, we’ll assume that you’re using IntelliJ, but other IDEs and editors probably use similar user interfaces. (You may need to create a new project or working directory (folder)).
Create a new file by going to File > New > Java class
Name it HelloWorld.java

Type the following code into the file:

public class HelloWorld {
 public static void main(String[] args) {
     // Prints Hello world! to the console
     System.out.println("Hello world!");
 }
}

Press the green play button next to public class HelloWorld. This should run your program and you should see this output:
```
Hello world!
```

Wow, you’ve just written your first few lines of Java code! Let’s break down what happened.

public class HelloWorld {
    ...
}

First, you declared a class called HelloWorld. We’re going to learn more about classes in Unit 5. For now, all you need to know is that all Java files contain a public class and the name of that class must match the file name exactly. (Notice that you created a file called HelloWorld.java.)

Also, everything inside of the class is contained within the curly braces. We’ll use curly braces to denote the start and end of a lot of things in Java.

Another thing to note is that class names are named in a special way such that each word in the class name is capitalized and there are no spaces between each word.

public class HelloWorld {
    public static void main(String[] args) {
        ...
    }
}

Inside of the HelloWorld class is the main method. Everything inside of the main method executes when you run your program.

You might be wondering what is the public static void or String[] args stuff is. We’ll get to that later, for now whenever you write a program, make sure you have a main method header that looks exactly like the one you just wrote.

public class HelloWorld {
    public static void main(String[] args) {
        // Prints Hello world! to the console
        System.out.println("Hello world!");
    }
}

As you may have noticed, the rest of the code is what actually does the magic of printing “Hello world!” to the console. We’ll talk more about what specifically those remaining 2 lines means in the next section.

Before we get to that, here are some things you should know about Java:

All Java statements end with a semicolon (for example, System.out.println("Hello world!");)
For the most part, whitespace (stuff without characters in it like spaces, empty lines, tabs, etc.) doesn’t matter in Java. However, you should indent properly (more on that later). For example, this:

public class HelloWorld {
    public static void main(String[] args) {
        // Prints Hello world! to the console
        System.out.println("Hello world!");
    }
}

is the same as this:

public class HelloWorld { public static void main(String[] args) {
// Prints Hello world! to the console
System.out.println("Hello world!");}}

It’s just a lot harder to read and is considered bad style. So make sure you leave whitespace appropriately and indent!

Speaking of hard to read, try to keep your lines of code within your frame of view (80 characters or less per line)

Note: From now on, in some code snippets, we will omit the class and main method declarations for brevity. Just know that in order for the program to actually work in real life, you’ll need both of these things.

Unit 1: Introduction to Java

Table of Contents

What is programming?

What is Java?

Your First Java Program