General Scala

• How do you pronouce Scala?
• The main version of Scala compiles to bytecode for which platform?
• How can you run Scala code?
• What is Scala’s primary build tool?
• What is the highest supertype of all Scala objects?
• What is the lowest subtype of all Scala objects?
• What is the difference between == and eq?
• Which packages are implicitly imported in every Scala source file?

Values, Variables and Control Structures

• What is the value and type of s below?

val moritz = 1865
val s = {
  "Max"
  moritz
}

• What is the value and type of result below?

val result = if (true) "blue" else 2

• What is the difference between a val and a var?

Collections

• Write an expression that gives the number of elements in xs.

val xs = Set( ... )

• Write an expression that creates a Map referenced by a val named langs such that

scala> langs("Lisp")
res0: String = John McCarthy

scala> langs("Java")
res1: String = James Gosling

scala> langs("Pascal")
res2: String = Niklaus Wirth

scala> langs("Scala")
res3: String = Martin Odersky

• Write a for-comprehension that uses langs from the previous question to create a Seq of the last names of the values in langs, that is, List(McCarthy, Gosling, Wirth, Odersky).

Functions

• Write a function called mean that takes a variable number of Double parameters and returns their arithmetic mean (sum divided by number of numbers).

• Given xs: List[Int], write an invocation of the filter method on xs that passes a function literal which selects only the odd numbers in xs.

• Write a function named listToString[T] that takes a single List[T] and returns a string representation of the List[T]. The listToString function should have a single expression which calls a nested helper function which is recursive and uses pattern matching to recursively accumulate a string representation. Your helper function may use an if statement instead of pattern matching for partial credit.

Classes and Objects

• Write the minimal Scala definition of a (non-case) class named Item which has two fields, name of type String and hauptstadt of type String.

• Write an equals method for the Item class above using the recipe we discussed in class.

• Write a hashCode method for the Item class above using the recipe we discussed in class.

• Write a companion object for the Item class above with a factory method that allows us to create an Item object with expression like Item("Key Lime", 3.14) (leaving off operator new).

Inheritance

Given the Person class below, write the minimal non-final subclass of Person named Employee that adds a mutable salary: Double field and initializes the fields defined in Person.

class Person(val name: String)

Case Classes and Pattern Matching

• Given the classes below, write a function named next which takes a single parameter fußgängerampel: AmpelMann and returns the next AmpelMann in the Grün -> Rot -> Grün cycle. Your next function body should be a single match expression.

sealed trait AmpelMann
case object Grün extends AmpelMann
case object Rot extends AmpelMann

Algebraic Data Types

• Write minimal traits/classes/case classes such that the following function would compile without warning or error, but if you removed one of the cases it would compile with a “match may not be exhaustive” warning.

def hauptstadt(land: Bundesland) = land match {
  case land: Berlin => "Berlin"
  case land: Brandenburg => "Potsdam"
  case land: MecklenburgVolpommern => "Schwerin"
  case land: SachsenAnhalt => "Magdeburg"
  case land: Sachsen => "Dresden"
  case land: SchleswigHolstein => "Kiel"
  case land: FreieHansestadtHamburg => "Hamburg"
  case land: HansestadtBremen => "Bremen"
  case land: Niedersachsen => "Hannover"
  case land: NordrheinWestfalen => "Düsseldorf"
  case land: FreistaatThüringen => "Erfurt"
  case land: Hessen => "Wiesbaden"
  case land: RheinlandPfalz => "Mainz"
  case land: Saarland => "Saarbrücken"
  case land: BadenWürttemberg => "Stuttgart"
  case land: FreistaatBayern => "München"
}