World.kt

import java.lang.RuntimeException
import java.util.Arrays

object VariantWorld2 {
    class Greet : World.Visitor {
        fun visit(subject: Dog, arg: String): String {
            return "$arg is greeted"
        }

        fun visit(subject: Cat, arg: String): String {
            return "$arg is greeted"
        }

        override fun visit(subject: World.Subject, arg: String): String {
            if (subject is Dog) {
                return subject.receive(this, arg)
            } else if (subject is Cat) {
                return subject.receive(this, arg)
            }
            throw RuntimeException();
        }
    }

    class Dog(name: String) : World.Animal(name) {

        fun receive(visitor: Greet, arg: String): String {
            return visitor.visit(this, this.name + ": Joyfully " + arg)
        }

        fun receive(visitor: Leave, arg: String): String {
            return visitor.visit(this, this.name + ": Sadly " + arg)
        }
    }

    class Cat(name: String) : World.Animal(name) {

        fun receive(visitor: Greet, arg: String): String {
            return visitor.visit(this, this.name + ": Sadly " + arg)
        }

        fun receive(visitor: Leave, arg: String): String {
            return visitor.visit(this, this.name + ": Joyfully " + arg)
        }
    }

    class Leave : World.Visitor {
        fun visit(subject: Dog, arg: String): String {
            return "$arg is left"
        }

        fun visit(subject: Cat, arg: String): String {
            return "$arg is left"
        }

        override fun visit(subject: World.Subject, arg: String): String {
            if (subject is Dog) {
                return subject.receive(this, arg)
            } else if (subject is Cat) {
                return subject.receive(this, arg)
            }
            throw RuntimeException();
        }
    }

    @JvmStatic
    fun main(args: Array<String>) {
        val fido = Dog("Fido")
        val garfield = Cat("Garfield")

        val greet = Greet()
        val leave = Leave()

        for (a in Arrays.asList(fido, garfield)) {
            for (v in Arrays.asList(greet, leave)) {
                System.out.println(v.visit(a, "bob"))
            }
        }
    }
}