Decorator Design Pattern - Kotlin

DecoratorDesignPattern.kt

class DecoratorDesignPattern {
    companion object {
        @JvmStatic
        fun main(args: Array<String>) {
            val rose = RoseBouquet()
            println("Without customization = ${rose.description}, ${rose.cost()}")
            val roseWrapper = PaperWrapper(rose)
            println("With customization = ${roseWrapper.description}, ${roseWrapper.cost()}")

            val orchid = OrchidBouquet()
            println("Without customization = ${orchid.description}, ${orchid.cost()}")
            val orchidRibbon = RibbonBow(orchid)
            println("With customization = ${orchidRibbon.description}, ${orchidRibbon.cost()}")
        }
    }
}

/**
 * Base class for our Design Pattern.
 */
abstract class FlowerBouquet {
    open var description: String = ""

    /*
    Child should override this method
     */
    abstract fun cost(): Double
}

/**
 * Extended from [FlowerBouquet]
 */
class RoseBouquet : FlowerBouquet() {
    override fun cost(): Double = 12.0

    init {
        description = "Rose bouquet"
    }
}

/**
 * Extended from [FlowerBouquet]
 */
class OrchidBouquet : FlowerBouquet() {
    override fun cost(): Double {
        return 29.0
    }

    init {
        description = "Orchid bouquet"
    }
}

/**
 * Here is the entry point for the Decorator Design Pattern.
 * We want to achieve run-time functionalities for [FlowerBouquet] objects.
 * All child that extend [FlowerBouquet] are eligible for this run-time functionalities.
 */
abstract class FlowerBouquetDecorator : FlowerBouquet() {
    abstract override var description: String
}

/**
 * Provide additional functionalities to [FlowerBouquet] objects.
 * [PaperWrapper] take [FlowerBouquet] object instance as parameter for rum-time behaviour changes.
 *
 * @param flowerBouquet [FlowerBouquet] instance
 */
class PaperWrapper(private var flowerBouquet: FlowerBouquet) : FlowerBouquetDecorator() {
    override var description: String = flowerBouquet.description + ", paper wrap"

    override fun cost(): Double {
        return 3 + flowerBouquet.cost()
    }
}

/**
 * Provide additional functionalities to [FlowerBouquet] objects.
 * [PaperWrapper] take [FlowerBouquet] object instance as parameter for rum-time behaviour changes.
 *
 * @param flowerBouquet [FlowerBouquet] instance
 */
class RibbonBow(private var flowerBouquet: FlowerBouquet) : FlowerBouquetDecorator() {
    override var description: String = flowerBouquet.description + ", ribbon bow"

    override fun cost(): Double {
        return 6.5 + flowerBouquet.cost()
    }
}