How to avoid large if-statements and instanceof

Question

Animal

public abstract class Animal {
 String name;

 public Animal(String name) {
  this.name = name;
 }

}

Lion<

Answer 1

Pattern matching support in the language eliminates the need for the ugly visitor pattern.

See this Scala code for example:

abstract class Animal(name: String)

class Lion(name: String) extends Animal(name) {
  def roar() {
    println("Roar!")
  }
}

class Deer(name: String) extends Animal(name) {
  def runAway() {
    println("Running!")
  }
}

object TestAnimals {
  def main(args: Array[String]) {
    val animals = List(new Lion("Geo"), new Deer("D1"), new Deer("D2"))
    for(animal <- animals) animal match {
      case l: Lion => l.roar()
      case d: Deer => d.runAway()
      case _       => ()
    }
  }
}