Реализации на Kotlin

Publisher-subscriber

Общая реализация на языке Kotlin

ISubscriber

interface ISubscriber {
    fun writeComment()
}

GoodSubscriber

class GoodSubscriber : ISubscriber {
    override fun writeComment() {
        println("Subscriber writes positive comment in comment section.")
    }
}

NeutralSubscriber

class NeutralSubscriber : ISubscriber {
    override fun writeComment() {
        println("Subscriber writes nothing.")
    }
}

BadSubscriber

class BadSubscriber : ISubscriber {
    override fun writeComment() {
        println("Subscriber writes negative comment in comment section.")
    }
}

Publisher

class Publisher {
    private val subs: MutableSet<ISubscriber> = mutableSetOf()

    fun subscribe(subscriber: ISubscriber): Boolean = subs.add(subscriber)

    fun unsubscribe(subscriber: ISubscriber): Boolean = subs.remove(subscriber)

    fun doAction() {
        println("Creating post")
        for (sub in subs)
            sub.writeComment()
    }
}

fun main() {
    val publisher = Publisher()

    val goodSubscriber = GoodSubscriber()
    val badSubscriber = BadSubscriber()
    val neutralSubscriber = NeutralSubscriber()

    publisher.subscribe(goodSubscriber)
    publisher.subscribe(badSubscriber)
    publisher.subscribe(neutralSubscriber)

    publisher.doAction()

    publisher.unsubscribe(badSubscriber)

    publisher.doAction()
}