First Programming Code

In this lesson, you will write your first programming code in Java. The goal is to write a program that prints the text Hello World! on execution. We will guide you through the process step by step.

Setting up for Coding

First, make sure that you have IntelliJ set-up. When working on a campus computer, this should already be the case. When working on your own computer, see the installation instructions for the necessary steps.

Next, download the code samples for this week from Canvas and open these in IntelliJ. The video below demonstrates you how to do this:

Note: an older version of IntelliJ is used in this video. If you are using the most recent version of IntelliJ, you can skip the steps from 0:15 to 0:32 in the video and follow these steps instead:

• Open the IntelliJ IDEA
• In the Welcome Screen, click on Learn in the menu on the left
• Click on Enable Access under the Learn to Program section
• Once it is finished, click on Get Started
• A new window pops up, in menu on the left go to My Courses
• At the bottom of the window, click on Open course from disk
• Select the zip-file that you downloaded and press Ok
• Click on Start in the new window that pops up
• IntelliJ may ask whether you trust the project. Click on Trust Project
• Select the Hello World task under the lesson First Programming Code

If you run into issues here, you can ask for help during the first week tutorial, on the discussion board.

Writing your first program

You are now ready to write your first program. In Java, programs require some mandatory code (known as boilerplate code) to indicate the program's name to the computer. Our program name is HelloWorld and has to correspond to the name of the file that contains the source code (i.e., HelloWorld.java).

public class HelloWorld {
    public static void main(String[] args) {
        // Code comes here
    }
}

Program execution begins after the line public static void main(String[] args) { and concludes at the final }. Although the template may seem overwhelming, it will become a familiar concept throughout the course. Note that, while our examples may not always display the template, it is actually required for every program file. As such, our examples might be a single line, such as example below illustrating the print command.

Actual code

Let's write our first code between the curly brackets in the example! We will consider the statement:

System.out.println("Hello World!");

Note that source code is read line-by-line, from left to right, with each statement ending with a semicolon (;).

The statement used in this program is specific to Java and outputs text to the console during program execution. The text to be printed is specified within the brackets, in this case Hello World!. Note that it's important to surround the printed text with quotation marks (""), which are not printed themselves.

When adding our cade to the template again, our code looks like this:

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

Running the code

You are now ready to run your code! To run this program, click on the green triangle has appeared in the margin and click on run. You can also use the keyboard shortcut Ctrl + Shift + F10. If you followed the above steps, you should now see that the text "Hello World!" is printed to the console, which you can read under the opened Run tab at the bottom of your screen. If you want to rerun your code, you can click on the green triangle in the top right corner, or use the keyboard shortcut Shift + F10.