嗨,我是Kotlin世界的新手。我喜欢我目前所看到的,并开始考虑将我们在应用程序中使用的一些库从Java转换为Kotlin。

这些库充满了带有setter、getter和Builder类的pojo。现在我已经在谷歌上找到了在Kotlin中实现Builders的最佳方法,但没有成功。

第二次更新:问题是如何写一个建设者设计模式的一个简单的pojo与一些参数在Kotlin?下面的代码是我尝试编写java代码,然后使用eclipse-kotlin-plugin转换为Kotlin。

class Car private constructor(builder:Car.Builder) {
    var model:String? = null
    var year:Int = 0
    init {
        this.model = builder.model
        this.year = builder.year
    }
    companion object Builder {
        var model:String? = null
        private set

        var year:Int = 0
        private set

        fun model(model:String):Builder {
            this.model = model
            return this
        }
        fun year(year:Int):Builder {
            this.year = year
            return this
        }
        fun build():Car {
            val car = Car(this)
            return car
        }
    }
}

当前回答

class Person(
    val name:String,
    val family:String,
    val age:Int,
    val nationalCode: String?,
    val email: String?,
    val phoneNumber: String?
) {

    // Private constructor
    private constructor(builder: Builder) : this (
        builder.name,
        builder.family,
        builder.age,
        builder.nationalCode,
        builder.email,
        builder.phoneNumber
    )

    // Builder class

    // 1 Necessary parameters in Builder class : name , family
    class Builder(val name :String,val family :String) {

        // 2 Optional parameters in Builder class :
        var age: Int = 0
            private set
        var nationalCode: String? = null
            private set
        var email: String? = null
            private set
        var phoneNumber: String? = null
            private set

        fun age(age: Int) = apply { this.age = age }
        fun nationalCode(nationalCode: String) =
            apply { this.nationalCode = nationalCode }
        fun email(email: String) = apply { this.email = email }
        fun phoneNumber(phoneNumber: String) =
            apply { this.phoneNumber = phoneNumber }

        // 3 Create
        fun create() = Person(this)

    }
}

存取资料:

val firstPerson = Person.Builder(
    name = "Adnan",
    family = "Abdollah Zaki")
    .age(32)
    .email("Adnan9011@gmail.com")
    .phoneNumber("+989333030XXX")
    .nationalCode("04400XXXXX")
    .create()

val secondPerson = Person.Builder(
    name = "Foroogh",
    family = "Varmazyar")
    .create()

其他回答

我刚刚发现了一个有趣的方法来创建kotlin构建器:

如您所见,moduleBuilder可以用于其他grafana构建。

代码如下:

class Grafana(
    private val module: String,
    private val scene: String,
    private val action: String,
    private val metric: String
) {
    companion object {
        fun build(module: String, scene: String, action: String, metric: String) =
            Grafana(module, scene, action, metric)

        val builder = ::build.curriedBuilder()

        private fun <P1, P2, P3, P4, R> Function4<P1, P2, P3, P4, R>.curriedBuilder() =
            fun(p1: P1) = fun(p2: P2) = fun(p3: P3) = fun(p4: P4) = this(p1, p2, p3, p4)
    }

    fun report() = Unit
}


val moduleBuilder = Grafana.builder("module")
val scene = moduleBuilder("scene")
val gfA = scene("action")("metric")
gfA.report()

val sceneB = moduleBuilder("sceneB")
val gfB = sceneB("action")("metric")
gfB.report()

val gfC = Grafana.builder("xx")("xxx")("xxxx")("xxxx")
gfC.report()

我迟到了。如果我必须在项目中使用Builder模式,我也遇到了同样的困境。后来,经过研究,我意识到这是完全不必要的,因为Kotlin已经提供了命名参数和默认参数。

如果你真的需要实施,Kirill Rakhman的答案是关于如何以最有效的方式实施的可靠答案。您可能会发现另一件有用的事情是https://www.baeldung.com/kotlin-builder-pattern,您可以将其与Java和Kotlin的实现进行比较和对比

class Foo private constructor(@DrawableRes requiredImageRes: Int, optionalTitle: String?) {

    @DrawableRes
    @get:DrawableRes
    val requiredImageRes: Int

    val optionalTitle: String?

    init {
        this.requiredImageRes = requiredImageRes
        this.requiredImageRes = optionalTitle
    }

    class Builder {

        @DrawableRes
        private var requiredImageRes: Int = -1

        private var optionalTitle: String? = null

        fun requiredImageRes(@DrawableRes imageRes: Int): Builder {
            this.intent = intent
            return this
        } 

        fun optionalTitle(title: String): Builder {
            this.optionalTitle = title
            return this
        }

        fun build(): Foo {
            if(requiredImageRes == -1) {
                throw IllegalStateException("No image res provided")
            }
            return Foo(this.requiredImageRes, this.optionalTitle)
        }

    }

}

对于简单类,不需要单独的构建器。您可以像Kirill Rakhman描述的那样使用可选的构造函数参数。

如果你有更复杂的类,那么Kotlin提供了一种方法来创建Groovy风格的Builders/DSL:

类型安全的建筑商

这里有一个例子:

Github示例-构建器/汇编器

现在的人们应该检查Kotlin的类型安全构建器。

使用上述方法创建对象将看起来像这样:

html {
    head {
        title {+"XML encoding with Kotlin"}
    }
    // ...
}

vaadin-on-kotlin框架是一个很好的“实际”使用示例,它利用类型安全构建器来组装视图和组件。