Question

I would like to check constructor arguments and refuse to construct throwing IllegalArgumentException in case the arguments set is not valid (the values don’t fit in expected constraints). And same check should work while setting same argument set while modifying the object. How to code this in Scala?

  scala> class Rectangle (var Length:Double, var Width:Double){
   | if (Length <0)
   | throw new IllegalArgumentException("The Length must be Non-negative")
   | if (Width <0)
   | throw new IllegalArgumentException("The Width must be Non-negative")
   | def setLength(l:Double) = Length = l
   | }
  defined class Rectangle

  scala> var R = new Rectangle (-9, -9)
  java.lang.IllegalArgumentException: The Length must be Non-negative
at Rectangle.<init>(<console>:9)

  scala> var R = new Rectangle (0, -9)
  java.lang.IllegalArgumentException: The Width must be Non-negative
at Rectangle.<init>(<console>:11)



   scala> var R = new Rectangle(9, 9)
   R: Rectangle = Rectangle@1590164


   scala> R.Length
   res7: Double = 9.0

   scala> R.Width
   res8: Double = 9.0

   scala> R.setLength(18)

   scala> R.Length
   res10: Double = 18.0

   scala> R.setLength(-9)
   // R.setLength should not the set the Length to -9.   **************************
   scala> R.Length
   res12: Double = -9.0

Answer 1

Must it be mutable?

case class Rectangle(length:Double, width:Double) {
  if (length < 0)
    throw new IllegalArgumentException("The Length must be Non-negative")
  if (width < 0)
    throw new IllegalArgumentException("The Width must be Non-negative")
  def setLength(l: Double) = copy(length=l)
}