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
}
}
}
我看到过许多将额外乐趣作为构建者的例子。我个人喜欢这种方法。节省编写构建程序的精力。
package android.zeroarst.lab.koltinlab
import kotlin.properties.Delegates
class Lab {
companion object {
@JvmStatic fun main(args: Array<String>) {
val roy = Person {
name = "Roy"
age = 33
height = 173
single = true
car {
brand = "Tesla"
model = "Model X"
year = 2017
}
car {
brand = "Tesla"
model = "Model S"
year = 2018
}
}
println(roy)
}
class Person() {
constructor(init: Person.() -> Unit) : this() {
this.init()
}
var name: String by Delegates.notNull()
var age: Int by Delegates.notNull()
var height: Int by Delegates.notNull()
var single: Boolean by Delegates.notNull()
val cars: MutableList<Car> by lazy { arrayListOf<Car>() }
override fun toString(): String {
return "name=$name, age=$age, " +
"height=$height, " +
"single=${when (single) {
true -> "looking for a girl friend T___T"
false -> "Happy!!"
}}\nCars: $cars"
}
}
class Car() {
var brand: String by Delegates.notNull()
var model: String by Delegates.notNull()
var year: Int by Delegates.notNull()
override fun toString(): String {
return "(brand=$brand, model=$model, year=$year)"
}
}
fun Person.car(init: Car.() -> Unit): Unit {
cars.add(Car().apply(init))
}
}
}
我还没有找到一种方法，可以强制在DSL中初始化一些字段，比如显示错误而不是抛出异常。如果有人知道就告诉我。
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()
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()
我个人从来没有在Kotlin见过一个建筑工人，但也许只有我这样。
所有需要的验证都发生在init块中:
class Car(val model: String,
val year: Int = 2000) {
init {
if(year < 1900) throw Exception("...")
}
}
在这里，我冒昧地猜测，您并不真的希望型号和年份可以更改。而且，这些默认值似乎没有任何意义，(特别是null作为name)，但为了演示目的，我留下了一个。
一个意见:
在Java中使用的构建器模式意味着不需要命名参数。在带有命名参数的语言(如Kotlin或Python)中，使用带有长串(可能是可选的)参数的构造函数是一个很好的实践。
我看到过许多将额外乐趣作为构建者的例子。我个人喜欢这种方法。节省编写构建程序的精力。
package android.zeroarst.lab.koltinlab
import kotlin.properties.Delegates
class Lab {
companion object {
@JvmStatic fun main(args: Array<String>) {
val roy = Person {
name = "Roy"
age = 33
height = 173
single = true
car {
brand = "Tesla"
model = "Model X"
year = 2017
}
car {
brand = "Tesla"
model = "Model S"
year = 2018
}
}
println(roy)
}
class Person() {
constructor(init: Person.() -> Unit) : this() {
this.init()
}
var name: String by Delegates.notNull()
var age: Int by Delegates.notNull()
var height: Int by Delegates.notNull()
var single: Boolean by Delegates.notNull()
val cars: MutableList<Car> by lazy { arrayListOf<Car>() }
override fun toString(): String {
return "name=$name, age=$age, " +
"height=$height, " +
"single=${when (single) {
true -> "looking for a girl friend T___T"
false -> "Happy!!"
}}\nCars: $cars"
}
}
class Car() {
var brand: String by Delegates.notNull()
var model: String by Delegates.notNull()
var year: Int by Delegates.notNull()
override fun toString(): String {
return "(brand=$brand, model=$model, year=$year)"
}
}
fun Person.car(init: Car.() -> Unit): Unit {
cars.add(Car().apply(init))
}
}
}
我还没有找到一种方法，可以强制在DSL中初始化一些字段，比如显示错误而不是抛出异常。如果有人知道就告诉我。
