如何在Kotlin中实现生成器模式?

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

一种方法是做以下事情:

class Car(
  val model: String?,
  val color: String?,
  val type: String?) {

    data class Builder(
      var model: String? = null,
      var color: String? = null,
      var type: String? = null) {

        fun model(model: String) = apply { this.model = model }
        fun color(color: String) = apply { this.color = color }
        fun type(type: String) = apply { this.type = type }
        fun build() = Car(model, color, type)
    }
}

使用示例:

val car = Car.Builder()
  .model("Ford Focus")
  .color("Black")
  .type("Type")
  .build()

2019-04-05 11:09:11

其他回答

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)
        }

    }

}

2018-05-25 21:59:16

一种方法是做以下事情:

class Car(
  val model: String?,
  val color: String?,
  val type: String?) {

    data class Builder(
      var model: String? = null,
      var color: String? = null,
      var type: String? = null) {

        fun model(model: String) = apply { this.model = model }
        fun color(color: String) = apply { this.color = color }
        fun type(type: String) = apply { this.type = type }
        fun build() = Car(model, color, type)
    }
}

使用示例:

val car = Car.Builder()
  .model("Ford Focus")
  .color("Black")
  .type("Type")
  .build()

2019-04-05 11:09:11

我在一个Kotlin项目中工作，该项目公开了一个由Java客户机使用的API (Java客户机不能利用Kotlin语言结构)。我们必须添加构建器以使它们在Java中可用，因此我创建了@Builder注释:https://github.com/ThinkingLogic/kotlin-builder-annotation 它基本上是Kotlin的Lombok @Builder注释的替代品。

2019-03-18 11:36:29

在kotlin中可以使用可选参数例子:

fun myFunc(p1: String, p2: Int = -1, p3: Long = -1, p4: String = "default") {
    System.out.printf("parameter %s %d %d %s\n", p1, p2, p3, p4)
}

然后

myFunc("a")
myFunc("a", 1)
myFunc("a", 1, 2)
myFunc("a", 1, 2, "b")

2017-05-24 01:49:55

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()

2022-04-26 09:52:45

如何在Kotlin中实现生成器模式?

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