Traits

trait Iterator[A] {
  def hasNext: Boolean
  def next(): A
}

trait Greeter {
  def greet(name: String): Unit
}

trait Greeter {
  def greet(name: String): Unit =
    println("Hello, " + name + "!")
}

class DefaultGreeter extends Greeter

class CustomizableGreeter(prefix: String, postfix: String) extends Greeter {
  override def greet(name: String): Unit = {
    println(prefix + name + postfix)
  }
}

val greeter = new DefaultGreeter()
greeter.greet("Scala developer") // Hello, Scala developer!

val customGreeter = new CustomizableGreeter("How are you, ", "?")
customGreeter.greet("Scala developer") // How are you, Scala developer?