//抽象组件
interface Coffee {

    fun getDesc(): String
    fun getCost(): Double

}

//具体组件
class SimpleCoffee: Coffee {

    override fun getDesc(): String = "[ simple coffee ]"
    override fun getCost(): Double = 6.0

}

//抽象装饰者
abstract class CoffeeDecorator(
    private val coffee: Coffee
): Coffee {

    override fun getDesc(): String = coffee.getDesc()
    override fun getCost(): Double = coffee.getCost()

}

//具体装饰者
class MikeDecorator(
    coffee: Coffee
): CoffeeDecorator(coffee) {

    override fun getDesc(): String = "${coffee.getDesc()}, mike"
    override fun getCost(): Double = coffee.getCost() + 2.0

}

//具体装饰者
class SugarDecorator(
    coffee: Coffee
): CoffeeDecorator(coffee) {

    override fun getDesc(): String = "${coffee.getDesc()}, sugar"
    override fun getCost(): Double = coffee.getCost() + 1.0

}

fun main() {
    val simpleCoffee = SimpleCoffee()
    println("simpleCoffee:")
    println("desc: ${simpleCoffee.getDesc()}")
    println("cost: ${simpleCoffee.getCost()}")

    //加奶
    val mikeSimpleCoffee = MikeDecorator(simpleCoffee)
    println("mikeSimpleCoffee:")
    println("desc: ${mikeSimpleCoffee.getDesc()}")
    println("cost: ${mikeSimpleCoffee.getCost()}")

    //加糖
    val mikeSugarSimpleCoffee = SugarDecorator(mikeSimpleCoffee)
    println("mikeSugarSimpleCoffee:")
    println("desc: ${mikeSugarSimpleCoffee.getDesc()}")
    println("cost: ${mikeSugarSimpleCoffee.getCost()}")

}

执行结果如下：

1.1.3、案例实现2

a）BlogShow 接口定义了一个博客展示的基础功能，BaseBlogShow 进行了实现.

//抽象构建角色
interface BlogShow {

    fun getTitle(): String
    fun getContent(): String
    fun display()

}

//具体构建角色
data class BaseBlogShow(
    private val title: String,
    private val content: String
): BlogShow {

    override fun getTitle() = title

    override fun getContent() = content

    override fun display() {
        println("title: $title")
        println("content: $content")
    }

}

b）BlogShowDecorator 是抽象装饰者，定义了规范，并且持有 blogShow 对象（抽象构建对象）.

FollowDecorator 和 VipDecorator 是具体装饰者，将来 BaseBlogShow 对象要进行动态扩展的时候，就可以将 BaseBlogShow 对象作为具体装饰者的构造参数，动态扩展.

//抽象装饰角色
abstract class BlogShowDecorator(
    protected val blogShow: BlogShow
): BlogShow {

    override fun getTitle() = blogShow.getTitle()
    override fun getContent() = blogShow.getContent()
    override fun display() = blogShow.display()

}

//具体装饰角色
class FollowDecorator(
    blogShow: BlogShow
): BlogShowDecorator(blogShow) {

    override fun display() {
        val title = super.getTitle()
        val content = if(super.getContent().length > 60)
            super.getContent().substring(0, 60).plus("...")
        else
            super.getContent()

        println("title: $title")
        println("content: $content")
        println("> 关注作者，查看更多内容！")
    }

}

//具体装饰角色
class VipDecorator(
    blogShow: BlogShow
): BlogShowDecorator(blogShow) {

    override fun display() {
        val title = super.getTitle()
        val content = if(super.getContent().length > 60)
           super.getContent().substring(0, 60).plus("...")
        else
           super.getContent()

        println("title: $title")
        println("content: $content")
        println("> 充值 vip，查看更多内容！")
    }

}

c）使用如下

fun main() {
    //假设从数据库中拿到数据
    val dbBlog = BaseBlogShow("Kotlin (programming language)", "Kotlin is a cross-platform, statically typed, general-purpose high-level programming language with type inference. Kotlin is designed to interoperate fully")
    //这里根据用户的权限来给文章进行不同的内容
    //...
    //假设用户未关注对方，但是对方的文章设置了关注才能访问
    //那么此处添加 "关注装饰器"
    var blog = FollowDecorator(dbBlog)
    //最后给该用户展示
    blog.display()
}

运行结果如下