Scala Tutorial - Scala Objects

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In Scala, we can use object to refer to an instance of a class as in Java and we can also use object as a keyword.

Singleton Objects

Scala does not have static members. Instead, Scala has singleton objects.

A singleton object definition looks like a class definition, except instead of the keyword class you use the keyword object.

A singleton is a class that can have only one instance.

For instance, we can create a singleton object to represent a Car like so:

object Car {
   def drive {
      println("drive car")
   }
}

With Car defined as an object, there can be only one instance of it, and we can call its methods just like static methods on a Java class:

Car.drive

Unlike classes, singleton objects cannot take parameter.

Note

We can use singleton objects for many purposes, including collecting related utility methods, or defining an entry point to a Scala application.

There are two ways to create a launching point for your application: define an object with a properly defined main method or define an object or that extends the App trait.

For the second approach, define an object that extends the App trait as shown here:

object Main extends App {
    println("Hello, world")
}

Scala provides a trait, scala.Application that your singleton object should extend for launching the application.

Then you place the code you would have put in the main method directly in the singleton object.

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