Creating a Thread (and Runnable) in Scala

By Alvin Alexander. Last updated: April 3, 2024

I ran into a strange problem this weekend where I noticed a huge difference between the way a Scala Future and a Thread worked for the exact same code. I think I’m pretty aware of the obvious differences between futures and threads, so this really caught me by surprise. If/when I figure out why there was such a difference in behavior for the given problem I’ll post that information here.

A Scala Thread example

While that problem will haunt me for a while, what I really want to post here today is a simple Scala Thread example:

// scala thread example
for (i <- 1 to 100) {
    val thread = new Thread {
        override def run {
            // your custom behavior here
        }
    }
    thread.start
    Thread.sleep(50) // slow the loop down a bit
}

As you can see, creating a Thread in Scala is just like creating a Thread in Java, with a few slight syntactical differences. The most important parts are to define your custom behavior in the run method, and to call start when you’re ready to start your thread.

A Java/Scala Runnable example

Of course you can also use a Java Runnable to create a Thread. I just typed the following code here and haven’t tested it, but a similar Runnable example will look something like this:

// define a scala runnable
class MyThread extends Runnable {

    def run {
        // your custom behavior here
    }

}

// start your runnable thread somewhere later in the code
new Thread(new MyThread)).start