CircleDemo.scala

// define a class called "Circle" 
// it has a 1-arg constructor that takes an Int
class Circle(r:Int) {
  // define a read-only field
  val radius = r;
  // define a method to compute diameter
  def diameter = radius * 2
  // define a method to compute area
  // we use braces since we need more than one line of code
  def area = {
    // declare a constant (think "val"ue)
    val pi = 3.14
    // declare a variable
    var area = pi * radius
    area *= radius
    // the braces are really an expression, and the
    // last statement dictates the value of the expression
    // so, no need to "return"
    area
  }
  // override a superclass method, like @Override in Java
  // we actually can't compile without this
  override def toString = "Circle with radius " + radius
}

// This is a type of static singleton; more on that later
object CircleDemo {
  def main(args: Array[String]) {
    // Create objects as in Java
    val circle = new Circle(4)
    println(circle.toString)
    println(circle.diameter)
    println(circle.radius)
    println(circle.area)
  }
}