Kotlin基础——优化设计模式

55 阅读 0 评论 0 点赞

设计模式

使用Kotlin优化Java的设计模式写法

创建型模式

工厂方法模式

interface Computer {
    val cpu: String
}

class PC(override val cpu: String = "Core") : Computer
class Server(override val cpu: String = "Xeon") : Computer

enum class ComputerType {
    PC, Server
}

class ComputerFactory {
    fun produce(type: ComputerType): Computer {
        return when (type) {
            ComputerType.PC -> PC()
            ComputerType.Server -> Server()
        }
    }
}

普通的工厂模式如上，调用时需要创建实例

val computer = ComputerFactory().produce(ComputerType.PC)

优化1：使用单例代替工厂类，使用object修饰

object ComputerFactory {
    fun produce(type: ComputerType): Computer {
        return when (type) {
            ComputerType.PC -> PC()
            ComputerType.Server -> Server()
        }
    }
}

这样就能省去创建过程，object会自动创建实例并调用

val computer = ComputerFactory.produce(ComputerType.PC)

优化2：使用operator重载invoke代替工厂方法名称

object ComputerFactory {
    operator fun invoke(type: ComputerType): Computer {
        return when (type) {
            ComputerType.PC -> PC()
            ComputerType.Server -> Server()
        }
    }
}

这样就能进一步省去创建过程，通过类名创建实例并调用

val computer = ComputerFactory(ComputerType.PC)

优化3：使用静态方法代替构造方法，将ComputerFactory移动到Computer接口里面

interface Computer {
    val cpu: String
    object Factory {
        operator fun invoke(type: ComputerType): Computer {
            return when (type) {
                ComputerType.PC -> PC()
                ComputerType.Server -> Server()
            }
        }
    }
}

这样就不是通过创建实例调用，而是通过静态方法调用

val computer = Computer.Factory(ComputerType.PC)

于此同时，如果我们是Computer接口的使用者，我们不必通过继承实现新方法，可以通过扩展函数

fun Computer.Factory.fromCPU(cpu: String): ComputerType? = when (cpu) {
    "Core" -> ComputerType.PC
    "Xeon" -> ComputerType.Server
    else -> null
}

抽象工厂模式

interface Computer
class Dell : Computer
class Asus : Computer
class Acer : Computer

abstract class AbstractFactory {
    abstract fun produce(): Computer
    companion object {
        operator fun invoke(factory: AbstractFactory): AbstractFactory {
            return factory
        }
    }
}

class DellFactory : AbstractFactory() {
    override fun produce() = Dell()
}
class AsusFactory : AbstractFactory() {
    override fun produce() = Asus()
}
class AcerFactory : AbstractFactory() {
    override fun produce() = Acer()
}

对于如上抽象工厂，调用时

val dellFactory = AbstractFactory(DellFactory())
val dell = dellFactory.produce()

优化1：使用内联函数代替抽象工厂创建过程

interface Computer
class Dell : Computer
class Asus : Computer
class Acer : Computer

abstract class AbstractFactory {
    abstract fun produce(): Computer
    companion object {
        inline operator fun <reified T : Computer> invoke(): AbstractFactory =
            when (T::class) {
                Dell::class -> DellFactory()
                Asus::class -> AsusFactory()
                Acer::class -> AcerFactory()
                else -> throw IllegalArgumentException()
            }
    }
}

class DellFactory : AbstractFactory() {
    override fun produce() = Dell()
}
class AsusFactory : AbstractFactory() {
    override fun produce() = Asus()
}
class AcerFactory : AbstractFactory() {
    override fun produce() = Acer()
}

在使用时，可通过类型参数确认工厂类型类型

 val dellFactory = AbstractFactory<Dell>()
 val dell = dellFactory.produce()

构建者模式

class Robot private constructor(
    val code: String,
    val battery: String?,
    val height: Int?,
    val weight: Int?
) {
    class Builder(val code: String) {
        private var battery: String? = null
        private var height: Int? = null
        private var weight: Int? = null
        fun setBattery(battery: String?): Builder {
            this.battery = battery
            return this
        }
        fun setHeight(height: Int): Builder {
            this.height = height
            return this
        }
        fun setWeight(weight: Int): Builder {
            this.weight = weight
            return this
        }
        fun build(): Robot {
            return Robot(code, battery, height, weight)
        }
    }
}

对于上面的Robot类存在三个可选属性，通过如下创建

val robot = Robot.Builder("001")
    .setBattery("A")
    .setHeight(100)
    .setWeight(80)
    .build()

优化1：通过默认参数代替可选参数

class Robot(
    val code: String,
    val battery: String? = null,
    val height: Int? = null,
    val weight: Int? = null
)

在创建时可省略后面的可选参数或者指定某个可选参数

val robot1 = Robot("001")
val robot2 = Robot("001", battery = "A")
val robot3 = Robot("001", height = 100, weight = 80)

若builder中对参数有约束调节，如机器人的重量需要根据电池决定，未传入就会抛出错误

fun build(): Robot {
    if (weight != null && battery == null) {
        throw IllegalArgumentException("When setting weight, the battery cannot be empty")
    }else{
        return Robot(code, battery, height, weight)

    }
}

可以同样在init中增加约束，其通过require实现（未达到条件则抛出异常，判断条件和上面相反）

class Robot(
    val code: String,
    val battery: String? = null,
    val height: Int? = null,
    val weight: Int? = null
) {
    init {
        require(weight == null || battery != null) {
            "When setting weight, the battery cannot be empty"
        }
    }
}

行为型模式

观察者模式

class StockUpdate : Observable() {
    val observers = mutableSetOf<Observer>()
    fun setStockChanged(price: Int) {
        observers.forEach {
            it.update(this, price)
        }
    }
}
class StockDisplay : Observer {
    override fun update(o: Observable?, price: Any?) {
        if (o is StockUpdate) {
            println("The lastest stock price is ${price}")
        }
    }

}

上面是Java标准库里面自带的观察者模式，调用如下

val su = StockUpdate()
val sd = StockDisplay()
su.observers.add(sd)
su.setStockChanged(100)

Observer 只有一个update方法，若有多个业务，则需要进行区分

优化1：通过委托代替观察者，参数为元数据KProperty、旧值、新值

interface StockUpdateListener {
    fun onRise(price: Int)
    fun onFall(price: Int)
}

class StockDisplay : StockUpdateListener {
    override fun onRise(price: Int) {
        println("The lastest stock price has rise to ${price}")
    }
    override fun onFall(price: Int) {
        println("The lastest stock price has fall to ${price}")
    }
}

class StockUpdate {
    var listeners = mutableListOf<StockUpdateListener>()
    var price: Int by Delegates.observable(0) { _, old, new ->
        listeners.forEach {
            if (new > old) it.onRise(price) else it.onFall(price)
        }

    }
}

当值发送改变会自动通知到观察者

val su = StockUpdate()
val sd = StockDisplay()
su.listeners.add(sd)
su.price = 100
su.price = 98

优化2：使用Vecoable对新值进行截获，初始值为0，只有正数时才能修改

var value: Int by Delegates.vetoable(0) { property, oldValue, newValue ->
    newValue > 0
}
value = 1
println(value)
value = -1
println(value)

策略模式

interface SwimStrategy {
    fun swim()
}
class Breaststroke : SwimStrategy {
    override fun swim() {
        println("Breaststroke")
    }
}
class Backstroke : SwimStrategy {
    override fun swim() {
        println("Backstroke")
    }
}
class Freestyle : SwimStrategy {
    override fun swim() {
        println("Freestyle")
    }
}

class Swimmer(val strategy: SwimStrategy) {
    fun swim() {
        strategy.swim()
    }
}

如上对于游泳，有不同的策略，在使用时指定算法

val weekendShaw = Swimmer(Freestyle())
weekendShaw.swim()
val weekdaysShaw = Swimmer(Breaststroke())
weekdaysShaw.swim()

优化1：使用高阶函数代替继承

fun breaststroke() {
    println("breaststroke")
}
fun backstroke() {
    println("backstroke")
}
fun freestyle() {
    println("freestyle")
}
class Swimmer(val swimming: () -> Unit) {
    fun swim() {
        swimming()
    }
}

使用时可通过方法引用，也可使用变量存储Lambda函数传入

val weekendShaw = Swimmer(::freestyle)
weekendShaw.swim()
val weekdaysShaw = Swimmer(::breaststroke)
weekdaysShaw.swim()

模板方法模式

abstract class CivicCenterTask {
    fun execute() {
        this.lineUp()
        this.askForHelp()
        this.evaluate()
    }
    private fun lineUp() {
        println("line up")
    }
    private fun evaluate() {
        println("evaluate")
    }
    abstract fun askForHelp()
}

class PullSocialSecurity : CivicCenterTask() {
    override fun askForHelp() {
        println("PullSocialSecurity")
    }
}

class ApplyForCitizenCard : CivicCenterTask() {
    override fun askForHelp() {
        println("ApplyForCitizenCard")
    }
}

如上，各个子类有不同的askForHelp()方法，调用时会根据方法实现各自的需求

val pss = PullSocialSecurity()
pss.execute()
val afcc = ApplyForCitizenCard()
afcc.execute()

优化1：使用高阶函数代替继承

class CivicCenterTask {
    fun execute(askForHelp: () -> Unit) {
        this.lineUp()
        askForHelp()
        this.evaluate()
    }
    private fun lineUp() {
        println("line up")
    }
    private fun evaluate() {
        println("evaluate")
    }
}
private fun pullSocialSecurity() {
    println("pullSocialSecurity")
}
private fun applyForCitizenCard() {
    println("ApplyForCitizenCard")
}

使用时传入方法引用

val task1 = CivicCenterTask()
task1.execute(::pullSocialSecurity)
val task2 = CivicCenterTask()
task1.execute(::applyForCitizenCard)

迭代器模式

通常实现迭代器模式可以通过实现Iterator接口

data class Book(val name: String)

class Bookcase(val books: List<Book>) : Iterator<Book> {
    private val iterator: Iterator<Book>
    init {
        this.iterator = books.iterator()
    }
    override fun hasNext() = this.iterator.hasNext()
    override fun next() = this.iterator.next()
}

遍历时

val bookcase = Bookcase(
    listOf(Book("A"), Book("B"))
)
for (book in bookcase) {
    println()
}

优化1：通过重载iterator()代替继承

class Bookcase(val books: List<Book>) {
    operator fun iterator(): Iterator<Book> = this.books.iterator()
}

优化2：通过扩展函数iterator()代替继承，适用于不能修改源码的情况

data class Book(val name: String)
class Bookcase(val books: List<Book>) {
}
operator fun Bookcase.iterator(): Iterator<Book> = this.books.iterator()

还可以通过object表达式来实现

operator fun Bookcase.iterator(): Iterator<Book> = object :Iterator<Book>{
    val iterator = books.iterator()
    override fun hasNext() = iterator.hasNext()
    override fun next() = iterator.next()
}

责任链模式

data class ApplyEvent(val money: Int)

interface ApplyHandler {
    val successor: ApplyHandler?
    fun handleEvent(event: ApplyEvent)
}

class GroupLeader(override val successor: ApplyHandler?) : ApplyHandler {
    override fun handleEvent(event: ApplyEvent) {
        when {
            event.money <= 100 -> println("GroupLeader yes")
            else -> when (successor) {
                is ApplyHandler -> successor.handleEvent(event)
                else -> throw IllegalStateException()
            }
        }
    }
}

class President(override val successor: ApplyHandler?) : ApplyHandler {
    override fun handleEvent(event: ApplyEvent) {
        when {
            event.money <= 500 -> println("President yes")
            else -> when (successor) {
                is ApplyHandler -> successor.handleEvent(event)
                else -> throw IllegalStateException()
            }
        }
    }
}

class College(override val successor: ApplyHandler?) : ApplyHandler {
    override fun handleEvent(event: ApplyEvent) {
        when {
            event.money <= 1000 -> println("College yes")
            else -> throw IllegalStateException()
        }
    }
}

上面是常见的责任链模式，通过判断传递事件

val college = College(null)
val president = President(college)
val groupLeader = GroupLeader(president)
groupLeader.handleEvent(ApplyEvent(10))
groupLeader.handleEvent(ApplyEvent(200))

优化1：通过偏函数简化责任链，定义如下，defineAt()和isDefinedAt()判断是否符合条件，f()处理事件，orElse()传递责任链

class PartialFunction<in P1, out R>(
    private val defineAt: (P1) -> Boolean,
    private val f: (P1) -> R
) {
     operator fun invoke(p1: P1): R {
        if (defineAt(p1)) {
            return f(p1)
        } else {
            throw  IllegalArgumentException()
        }
    }
    fun isDefinedAt(p1: P1) = defineAt(p1)
}

infix fun <P1, R> PartialFunction<P1, R>.orElse(that: PartialFunction<P1, R>): PartialFunction<P1, R> {
    return PartialFunction({ this.isDefinedAt(it) || that.isDefinedAt(it) }) {
        when {
            this.isDefinedAt(it) -> this(it)
            else -> that(it)
        }
    }
}

责任链定义如下，每一个责任链都是PartialFunction，传入判断条件和处理过程

data class ApplyEvent(val money: Int)

val groupLeader = {
    val defineAt: (ApplyEvent) -> Boolean = { it.money <= 100 }
    val handler: (ApplyEvent) -> Unit = { println("groupLeader yes") }
    PartialFunction(defineAt, handler)
}()

val president = {
    val defineAt: (ApplyEvent) -> Boolean = { it.money <= 500 }
    val handler: (ApplyEvent) -> Unit = { println("president yes") }
    PartialFunction(defineAt, handler)
}()

val college = {
    val defineAt: (ApplyEvent) -> Boolean = { true }
    val handler: (ApplyEvent) -> Unit = {
        when {
            it.money < 1000 -> println("college yes")
            else -> println("college no")
        }
    }
    PartialFunction(defineAt, handler)
}()

调用过程如下，通过orElse()传递责任链

val applyChain = groupLeader orElse president orElse college
applyChain(ApplyEvent(600))

状态模式

优化1：采用密封类来约束状态

结构型模式

装饰器模式

优化1：使用委托简化装饰过程

interface MacBook {
    fun getCost(): Int
    fun getDesc(): String
    fun getProdDate(): String
}

class MacBookPro : MacBook {
    override fun getCost() = 10000
    override fun getDesc() = "MacBookPro"
    override fun getProdDate() = "2022"
}

class ProcessorUpgradeMacbookPro(val macBook: MacBook) : MacBook by macBook {
    override fun getCost() = macBook.getCost() + 2000
    override fun getDesc() = macBook.getDesc() + ",+1G Memory"
}

如上，ProcessorUpgradeMacbookPro只需要复写需要的方法，其他方法调用时会自动委托给macBook变量

val macbookPro = MacBookPro()
val processorUpgradeMacbookPro = ProcessorUpgradeMacbookPro(macbookPro)
println(processorUpgradeMacbookPro.getCost())
println(processorUpgradeMacbookPro.getDesc())

优化2：通过扩展代替装饰者

class Printer{
    fun drawLine(){
        println("————————————")
    }
    fun drawDottedLine(){
        println("------------")
    }
    fun drawStars(){
        println("************")
    }
}

如对上面的类，利用扩展函数装饰方法，调用前后输出字符串

fun Printer.startDraw(decorated: Printer.() -> Unit){
    println("start drawing")
    decorated()
    println("end drawing")
}

调用过程如下

Printer().run {
    startDraw { drawLine() }
    startDraw { drawDottedLine() }
    startDraw { drawStars() }
}

本站资源均来自互联网，仅供研究学习，禁止违法使用和商用，产生法律纠纷本站概不负责！如果侵犯了您的权益请与我们联系！

转载请注明出处：免费源码网-免费的源码资源网站 » Kotlin基础——优化设计模式

点赞(0) 打赏

本文分类：文章资讯
本文标签：Kotlin基础——优化设计模式
浏览次数：55 次浏览
本文链接：https://freeymw.com/article/13235.html

上一篇 > PCL 点云RANSAC+SVD提取平面
下一篇 > kotlin 中的布尔

评论列表共有 0 条评论

暂无评论