01 Scala Principles 01 Session 01 First Steps Exercise

Exercises: A Simple Calculator

In this first exercise you will put altogether you have learned so far. Instead of worksheets you will put your code into classes and objects. You will also define a Scala singleton object with a main method allowing you to start it as a Scala application.

In the code skeletons you will find an object definition with a main method. In your IDE just do a right click > Run As > Scala Application

Example: main() method for starting as a Scala Application

object ScalaApp {
  def main(args: Array[String]) {
    val instance = new ScalaFun
    println("> " + instance + ": " + ScalaFun.dateFormat.format(instance.constructionTime))
  }
}

Objects

Now let's test your skill so far and free your limitations as a Java developer and introduce object classes ;)

Example: Definition and Construction

  object ScalaFun1
  object ScalaFun2 {}
  object ScalaFun3 { val message = "Hello, Scala" }
  ScalaFun3.message                               //> res0: String = Hello, Scala
  //compile error, since other constructor definitions are not allowed
  object ScalaFun4 {
    var message = "Hello, Scala"
    def this(anotherMessage: String) {
      this()
      this.message = anotherMessage
    }
  }

Calculator

Let's get back to elementary school. Remember you always like to cheat and use your calculator instead of your useless brain? Now is your chance... Implement a calculator with the operators add, minus, multiply and divide.

Example: Skeleton from the exercise

object Calculator {
  def add(a: Double, b: Double) = ???

  def subtract(a: Int, b: Double) = ???

  def multiply(a: Double, b: Double) = ???

  def divide(a: Double, b: Double) = ???
  
}

Resources

Classes and Case Classes

• Classes: http://docs.scala-lang.org/tutorials/tour/classes.html
• Case Classes: http://docs.scala-lang.org/tutorials/tour/case-classes.html