Data Types

Every value in Scala has a type. The basic types are:

@main def types(): Unit =
  val count: Int = 42
  val population: Long = 8_100_000_000L
  val price: Double = 19.99
  val isOpen: Boolean = true
  val grade: Char = 'A'
  val name: String = "Ada"

  println(s"$count $population $price $isOpen $grade $name")
  println(Int.MaxValue)
  println(Int.MaxValue + 1)

42 8100000000 19.99 true A Ada
2147483647
-2147483648

• Underscores make long numbers readable: 8_100_000_000L.
• L marks a Long literal.
• Int has limits: going past Int.MaxValue wraps around to a negative number silently. Use Long or BigInt for large values.

Everything is an object

Even numbers have methods:

@main def methodsOnValues(): Unit =
  println((-5).abs)
  println(3.max(7))
  println(10.toDouble)
  println(3.99.toInt)
  println('a'.toUpper)
  println("42".toInt + 1)

5
7
10.0
3
A
43

Converting with toInt on a Double truncates (3.99 → 3). Converting a String that isn't a number throws an error — the Option lesson shows the safe way.

The type hierarchy

At the top is Any. Below it, AnyVal covers values like Int and Boolean, and AnyRef covers objects like String and List. At the bottom, Nothing is the type of expressions that never return (like throwing an exception).