Ok Java is a little different than R or Python in that in order to run any code you have to first create a class object. I haven’t yet written a tutorial on classes and inheritence which form the basis of Object Oriented Programming.

If you’re trying to learn Java coming from Python or R this fact will be very disorienting as you can’t can’t just type some lines and run them at the command line. In Java you have to create a class first and then create a main method which will run the lines of code you want after you compile the code.

Each class must be stored in its on file as well. This means that everytime you want to create a new class you have to create a new file that has the same file name as the class name. The file name also has to end in .java just like all Python scripts have to end in .py. It’s a lot to take in that I will explain further in my tutorial on installing Java, but as of right now let’s just write a simple Hello World program.

// Java uses camelCase for its naming conventions. Awful I know.
// unlike Python, Java doesn't care about whitespace so you can
// structure your code however you want as each line ends with a
// semicolon.
public class helloWorld {

    // the main method will always look like this
    public static void main(String[] args) {
        //Look at all that just to print. Also don't forget your semicolon!
        System.out.println("Hello World");

Now your program is ready to compile so save it as helloWorld.java and then type at the command line java helloWorld.java and the output will be Hello World.