Hello World in Scala

Welcome to the Hello World in Scala page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

object HelloWorld extends App {
  println("Hello, World!")
}

Hello World in Scala was written by:

• Jeremy Griffith

This article was written by:

• Jeremy Grifski
• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

Up first, we have the class definition much like Java. However, there are two interesting keywords here: object and extends.

In Java, we would typically define a class using the class keyword. In fact, we normally even do that in Scala, so what's with this object keyword? Well, as it turns out, object is used when we want to define a singleton.

In object-oriented languages, a singleton is an object which has a one and only one policy. In other words, only one instance of the object will ever exist. Personally, I've only ever used the singleton design pattern to track state in a video game. Beyond that, I would consider it an anti-pattern.

That said, singletons are a feature in Scala, and they're typically used to define static functions. In other words, singletons can be used to generate utility classes that don't need to be instantiated to access their functionality.

In addition, singletons in Scala are often used as companion objects, but I can't say I totally understand what that is. Let me know in the comments.

Anyway, in this case, our singleton also extends App. This allows us to bypass the creation of a main method. We could have just as easily implemented Hello World in Scala as follows:

object HelloWorld {
    def main(args: Array[String]): Unit = {
        println("Hello, World!");
    }
}

At this point, we have something reminiscent of Java. Of course, the syntax is a bit different, but it looks about the same if we squint hard enough.

Finally, the only thing we have left is the print statement which is pretty typical at this point. Not much of a surprise there!

How to Run the Solution

If we want to try the code above, we can use an online Scala compiler. Just take the code above and drop it into the editor before hitting run.

Alternatively, we can always try to run the code locally. First, we'll need to follow the directions when downloading and installing Scala. Then, we'll probably want to get a copy of the solution.

With the heavy lifting out of the way, we should be able to simply run the following commands from the command line:

scalac hello-world.scala
scala hello-world

As we can see, Scala can be executed in pretty much the same way as Java. If all goes well, the last command should print the "Hello, World!" string.