Kotlin学习 6

基哥的奋斗历程2024-02-22 13:44

1.接口

Kotlin 复制代码 
interface Movable {
    var maxSpeed: Int
    var wheels: Int

    fun move(movable: Movable): String

}

class Car(var name: String, override var wheels: Int = 4, _maxSpeed: Int) : Movable {

    override var maxSpeed: Int = _maxSpeed
        get() = field
        set(value) {
            field = value
        }

    override fun move(movable: Movable): String {
        TODO("Not yet implemented")
    }

}

fun main() {
    val car = Car("1",4,8)

    println(car.maxSpeed)
}

1.1 接口属性默认实现

Kotlin 复制代码 
interface Movable {
    val maxSpeed: Int
       get() = (1..500).shuffled().first()//相当于给这个属性赋值  每次不一样但他不是修改它 只是修改了它的get方法 所有只读变量不可赋值

    var wheels: Int

    fun move(movable: Movable): String

}

class Car(var name: String, override var wheels: Int = 4) : Movable {

    override val maxSpeed: Int
        get() = super.maxSpeed


    override fun move(movable: Movable): String {
        TODO("Not yet implemented")
    }

}

fun main() {
    val car = Car("1",4)

    println(car.maxSpeed)
    println(car.maxSpeed)
    println(car.maxSpeed)
    println(car.maxSpeed)
}

2.抽象类

Kotlin 复制代码 
abstract class Gun(val  range:Int){
    abstract fun pullTrigger():String
}


abstract class Gun1(val  a:Int){
    abstract fun pullTrigger():String
}
class AK47(val price:Int):Gun(range = 80),Movable{
    override fun pullTrigger(): String {
        return "AK47 shooting"
    }

    override var wheels: Int
        get() = TODO("Not yet implemented")
        set(value) {}


}

3.泛型

Kotlin 复制代码 
class MagicBox<T> (item:T){
     var subject:T = item


}

class Boy(val name:String,val age:Int)

class Dog(val weight:Int)

fun main() {

    val magicBox1 = MagicBox(Boy("Jack", 20))
    val magicBox2 = MagicBox(Dog( 20))
    println(magicBox1.subject is Boy)
    println(magicBox2.subject is Dog)

}

4.泛型函数

Kotlin 复制代码 
class MagicBox<T> (item:T){
     var subject:T = item

    var available = false

    fun fetch():T?{
        return subject.takeIf { available } //true返回 this false返回null
    }

}

class Boy(val name:String,val age:Int)

class Dog(val weight:Int)

fun main() {

    val magicBox1 = MagicBox(Boy("Jack", 20))
    val magicBox2 = MagicBox(Dog( 20))
    magicBox1.available =true
    println(magicBox1.fetch())
   magicBox2.available=true
    println(magicBox2.fetch())
    magicBox2.fetch()?.run {
        println("you find $weight")
    }
}

5.多泛型参数

Kotlin 复制代码 
class MagicBox<T>(item: T) {
    var subject: T = item

    var available = false

    fun fetch(): T? {
        return subject.takeIf { available } //true返回 this false返回null
    }

    //return -> R
    fun <R> fetch(subjectModFunction: (T) -> R): R? {
        return subjectModFunction(subject).takeIf { available }
    }
}

class Boy(val name: String, val age: Int)

class Dog(val weight: Int)

fun main() {

    val magicBox1 = MagicBox(Boy("Jack", 20))

    magicBox1.available =true
    val fetch = magicBox1.fetch {
        Boy("男人", 30)
    }
    println(fetch)
    println(fetch?.name)
    println(fetch?.age)
}

6.泛型类型的约束

7. vararg关键字与get函数

vararg相当于Java的可变参数 Int ... age 类似效果

Kotlin 复制代码 
class MagicBox<T:Human>( vararg item: T) {
    var subject: Array<out T> = item

    var available = false

    fun fetch(index:Int): T? {

        return subject[index].takeIf { available } //true返回 this false返回null
    }

    //return -> R
    fun <R> fetch(index: Int,subjectModFunction: (T) -> R): R? {

        return subjectModFunction(subject[index]).takeIf { available }

    }
}
open class  Human(val age:Int)

class Boy(val name: String, age: Int):Human(age)

class Dog(val weight: Int)

fun main() {

    val magicBox1 = MagicBox(Boy("Jack0", 20),Boy("Jack1", 20),Boy("Jack2", 20),Boy("Jack3", 20))

    magicBox1.available =true
    val fetch = magicBox1.fetch(3) {
        it
    }
    println(fetch)
    println(fetch?.name)
    println(fetch?.age)
}

8.get函数

也就是运算符重载

Kotlin 复制代码 
class MagicBox<T:Human>( vararg item: T) {
    var subject: Array<out T> = item

    var available = false

    fun fetch(index:Int): T? {

        return subject[index].takeIf { available } //true返回 this false返回null
    }

    //return -> R
    fun <R> fetch(index: Int,subjectModFunction: (T) -> R): R? {

        return subjectModFunction(subject[index]).takeIf { available }

    }

    operator fun get(index: Int):T?{
        return subject[index]
    }

}
open class  Human(val age:Int)

class Boy(val name: String, age: Int):Human(age)

class Dog(val weight: Int)

fun main() {

    val magicBox1 = MagicBox(Boy("Jack0", 20),Boy("Jack1", 20),Boy("Jack2", 20),Boy("Jack3", 20))

    magicBox1.available =true
    val fetch = magicBox1.fetch(3) {
        it
    }
    println(fetch)
    println(fetch?.name)
    println(fetch?.age)

    println(magicBox1[3]?.name)
}

9. out 协变 in 逆变 invariant(不变)

Kotlin 复制代码 
//out
interface Production<out T> {
    fun product(): T
}

//in
interface Consumer<in T> {
    fun consume(item: T)
}

//不变
interface ProductionConsumer<T> {
    fun product(): T
    fun consume(item: T)
}


open class Food

open class FastFood : Food()

class Burger : FastFood()

//汉堡生产者
//食品商店
class FoodStore : Production<Food> {
    override fun product(): Food {
        println("Product Food")
        return Food()
    }

}


class FastFoodStore : Production<FastFood> {
    override fun product(): FastFood {
        println("Product FastFood")
        return FastFood()
    }

}

class BurgerStore : Production<Burger> {
    override fun product(): Burger {
        println("Product Burger")
        return Burger()
    }

}

//消费者
class EveryBody : Consumer<Food> {
    override fun consume(item: Food) {
        println("consume food")
    }

}

class ModernPeople : Consumer<FastFood> {
    override fun consume(item: FastFood) {
        println(item is Burger)
        println("consume FastFood")
    }

}

class AmericanPeople : Consumer<Burger> {
    override fun consume(item: Burger) {
        println("consume Burger")
    }

}

fun main() {
    //赋值
    val production1: Production<Food> = FoodStore()

    val product = production1.product()
    //用了Out关键字   子类转父类泛型         泛型可以协变和逆变
    val production2: Production<Food> = FastFoodStore()
    val production3: Production<Food> = BurgerStore()


    //in  父类转子类泛型
    val consumer1: Consumer<Burger> = EveryBody()
    val consumer2: Consumer<Burger> = ModernPeople()
    consumer2.consume(Burger())
    val consumer3: Consumer<Burger> = AmericanPeople()


}

10. reified关键字

reified 和 inline 关键字配合使用能够实现泛型类型判断。因为匿名函数会被优化到这个随机类型函数中，那么就能够知道具体类型是啥了

这个函数的返回类型由backup函数的返回类型决定 和类定义的泛型无关 也就是类的泛型没有起到任何约束作用 你写一个String都可以

Kotlin 复制代码 
class MagicBox<T : Human>() {

    //产生一个指定类型的对象，如果不是指定类型的对象，就通过backup函数生成一个指定类型的对象
//    fun <T> randomOrBackUp(backup: () -> T): T {
//        val items:List<out Human>  = listOf(
//            Boy("Jack", 20),
//            Man("John", 35)
//        )
//        val random:Human =items.shuffled().first()
//        return if (random is T){  //T会被擦除
//            random
//        }else{
//            backup()
//        }
//
//    }
    inline fun <reified T> randomOrBackUp(backup: () -> T): T { //内联函数它就会被替换，泛型擦除从而解决 类型将会保留下来

        val items:List<Human>  = listOf(
            Boy("Jack", 20),
            Man("John", 35)
        )
        val random:Human =items.shuffled().first()
        return if (random is T){  //T会被擦除
            random
        }else{
            backup()
        }

    }

}

open class Human(val age: Int)

class Boy(val name: String, age: Int) : Human(age){

}

class Man(val name: String, age: Int) : Human(age){
    override fun toString(): String {
        return "Man(name='$name' age ='$age')"
    }
}

fun main() {
      val box1:MagicBox<Boy> = MagicBox()
    val subject:Man = box1.randomOrBackUp {
        Man("Jimmy", 36)
    }
    println(subject)
}

11.定义扩展函数

Kotlin 复制代码 
//给字符串追加若干个感叹号
fun String.addExt(amount:Int =1 ):String{
    return this + "!".repeat(amount)
}

fun main() {
    println("abc".addExt(3))
}
Kotlin 复制代码 
//给字符串追加若干个感叹号
fun String.addExt(amount:Int =1 ):String{
    return this + "!".repeat(amount)
}

fun Any.easyPring(){
    println(this)
}
fun Any.easyPring1(){
    println(this.toString()+1)
}

fun main() {
    println("abc".addExt(3))

    "abc".easyPring()
}

可以用private修饰符，只能在此文件下使用

12.泛型扩展函数

Kotlin 复制代码 
//给字符串追加若干个感叹号
fun String.addExt(amount:Int =1 ):String{
    return this + "!".repeat(amount)
}

private fun <T> T.easyPring():T{
    println(this)
    return this;
}
fun Any.easyPring1(){
    println(this.toString()+1)
}

fun main() {
    println("abc".addExt(3))

     "abc".easyPring().addExt(3).easyPring()
}

13.扩展属性

Kotlin 复制代码 
val String.numVowels
        get() = count{ "aeiou".contains(it) }//true 计数器加1 

fun <T> T.easyPrint():T{
    println(this)
    return this
}

fun main() {
    "The people's Republic of China".numVowels.easyPrint()
    val count = "the".count()
    println(count)

}

14. 可空类型扩展函数

Kotlin 复制代码 
fun String?.printWithDefault (default:String) = print(this ?: default)//如果为null就为default


fun main() {
    val  nullableString :String?  = "asdas";
    nullableString.printWithDefault("jmj")
}

15. infix关键字

Kotlin 复制代码 
 infix fun String?.printWithDefault (default:String) = print(this ?: default)//infix 对一个参数的函数 可以简化写法，去掉调用的点和括号


fun main() {
    val  nullableString :String?  = "asdas";
    nullableString printWithDefault "jmj" 
}

16.定义扩展文件

Kotlin 复制代码 
package com.jason.kotlin.extension

fun <T> Iterable<T>.randomTask():T = this.shuffled().first()
Kotlin 复制代码 
import com.jason.kotlin.extension.randomTask

fun main() {
    val randomTask = listOf<String>("jmj", "sada", "asd").randomTask()
    println(randomTask)
}
相关推荐
LUCIAZZZ2 分钟前
简单说一下什么是RPC
java·网络·网络协议·计算机网络·spring cloud·rpc
嘵奇5 分钟前
最新版IDEA下载安装教程
java·intellij-idea
s_fox_31 分钟前
Nginx Embedded Variables 嵌入式变量解析(4)
java·网络·nginx
Jelena1577958579237 分钟前
使用Java爬虫获取1688 item_get_company 接口的公司档案信息
java·开发语言·爬虫
数据小小爬虫40 分钟前
Jsoup解析商品详情时，如何确保数据准确性？
java·爬虫
V+zmm101341 小时前
自驾游拼团小程序的设计与实现（ssm论文源码调试讲解）
java·数据库·微信小程序·小程序·毕业设计
坚定信念，勇往无前1 小时前
springboot单机支持1w并发，需要做哪些优化
java·spring boot·后端
丁总学Java1 小时前
`AdminAdminDTO` 和 `userSession` 对象中的字段对应起来的表格
java
xvch2 小时前
Kotlin 2.1.0 入门教程（二十三）泛型、泛型约束、协变、逆变、不变
android·kotlin
陈无左耳、2 小时前
HarmonyOS学习第2天: 解锁语言与框架的无限可能
学习·华为·harmonyos
热门推荐
01本地部署DeepSeek教程（Mac版本）02如何在WPS和Word/Excel中直接使用DeepSeek功能03DeepSeek本地部署详细指南04太炸裂了！清华大学deepseek从入门到精通使用手册又出第三版了，《普通人如何抓住DeepSeek红利》（无套路，直接下载）05DeepSeek各版本说明与优缺点分析06DeepSeek r1本地安装全指南07本地化部署AI知识库：基于Ollama+DeepSeek+AnythingLLM保姆级教程08DeepSeek R1本地化部署 Ollama + Chatbox 打造最强 AI 工具09在Windows下安装Ollama并体验DeepSeek r1大模型10Page Assist - 本地Deepseek模型 Web UI 的安装和使用