Steps

1. How to declare a Singleton Object

In the previous tutorials, we've actually made use of Singleton Objects without even mentioning it! So as a reminder, to create Singleton Objects in Scala, you need to make use of the keyword object as shown below.

println("Step 1: How to declare a Singleton Object")
object DonutShoppingCartCalculator {

}

2. How to define a global field

If you have used another programming language such as Java or .NET, you would perhaps expect that Scala also has the keyword static which would allow you to declare global fields and constants.

But, Scala does not have a static keyword! Instead, you can simply encapsulate a global field using the val keyword inside a Singleton Object.

println("Step 1: How to declare a Singleton Object")
object DonutShoppingCartCalculator {

 println("\nStep 2: How to define a global field")
 val discount: Double = 0.01
}

NOTE:

• Perhaps in a real application, you would not hard-code a discount value. But, we're just showing here how to expose a discount field globally.

3. How to define utility function called calculateTotalCost

Once again as mentioned in Step 2 above, Scala does not exposed a static keyword. But you can encapsulate functions and methods inside a Singleton Object if you would like to expose some globally accessible utility function or method.

println("Step 1: How to declare a Singleton Object")
object DonutShoppingCartCalculator {

 println("\nStep 2: How to define a global field")
 val discount: Double = 0.01

 println("\nStep 3: How to define utility function called calculateTotalCost")
 def calculateTotalCost(donuts: List[String]): Double = {
  // calculate the cost of donuts
  return 1
 }
}

NOTE:

• In a real application, the calculateTotalCost() function would have other parameters required to calculate the total cost of donuts in a shopping cart.
• You can always review the tutorials on functions if you are unclear about how to create and use functions in Scala.

4. How to call global discount field from Step 2

To access a global field, you simply call the Singleton Object with the dot operator and followed by the global field.

println("\nStep 4: How to call global discount field from Step 2")
println(s"Global discount = ${DonutShoppingCartCalculator.discount}")

You should see the following output when you run your Scala application in IntelliJ:

Step 4: How to call global discount field from Step 2
Global discount = 0.01

5. How to call the utility function calculateTotalCost from Step 3

To access a global utility function or method, you simply call the Singleton Object with the dot operator and followed by the utility function or method.

println("\nStep 5: How to call the utility function calculateTotalCost from Step 3")
println(s"Call to calculateTotalCost function = ${DonutShoppingCartCalculator.calculateTotalCost(List())}")

You should see the following output when you run your Scala application in IntelliJ:

Step 5: How to call the utility function calculateTotalCost from Step 3
Call to calculateTotalCost function = 1.0