cheat.sheets/sheets/_scala/ObjectOrientation

// constructor params - private
class C(x: R) // same as
class C(private val x: R)
var c = new C(4)

// constructor params - public
class C(val x: R)
var c = new C(4)
c.x

class C(var x: R) {
  // constructor is class body
  assert(x > 0, "positive please")
  //
  // declare a public member
  var y = x
  //
  // declare a gettable but not settable member
  val readonly = 5
  //
  // declare a private member
  private var secret = 1
  //
  // alternative constructor
  def this = this(42)
}   

// anonymous class
new{ ... }

// define an abstract class. (non-createable)
abstract class D { ... }

// define an inherited class.
class C extends D { ... }
class D(var x: R)

// inheritance and constructor params. (wishlist: automatically pass-up params by default)
class C(x: R) extends D(x)

// define a singleton. (module-like)
object O extends D { ... }

// traits.
trait T { ... }

// interfaces-with-implementation. no constructor params
// mixin-able: http://docs.scala-lang.org/tutorials/tour/mixin-class-composition.html
class C extends T { ... }
class C extends D with T { ... }

// multiple traits.
trait T1; trait T2
class C extends T1 with T2
class C extends D with T1 with T2

// must declare method overrides.
class C extends D { override def f = ...}

// create object.
new java.io.File("f")

new List[Int] // BAD type error: abstract type
List(1,2,3) // GOOD instead, convention: callable factory shadowing the type

// class literal.
classOf[String]

// type check (runtime)
x.isInstanceOf[String]

// type cast (runtime)
x.asInstanceOf[String]

// ascription (compile time)
x: String