Kotlin keyword extension function

@[TOC](kotlin keyword spread function )

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Preface

Use pure code Add The way of annotating , You can understand the source code faster
If you like , Please give me a compliment , In the later stage, we will continue to explain in depth

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1、reified keyword

// 1、 Create three new data classes , Used to randomly generate objects // 2、randomOrDefault()  function , Backup mechanism Lambda// 3、 Randomly generate one   object // <ObjectClass1>  Specified objects     TestClass().randomOrDefault<ObjectClass1> {        println(" Due to randomly generated objects   It's different from what we specified , Enable alternate objects ")        ObjectClass1(" Alternate objects , King five ", 99)    }data class ObjectClass1(val name: String, val age: Int)data class ObjectClass2(val name: String, val age: Int)data class ObjectClass3(val name: String, val age: Int)class TestClass {//  All functions , It's all written on the function //  By default, an object is output randomly , If this object is inconsistent with the specified object , Enable alternate objects , Otherwise, the object is returned directly    inline fun <reified T> randomOrDefault(defaultLambdaAction:() ->T) : T? {        val objList = listOf(            ObjectClass1("obj1 tiger", 18), ObjectClass2("obj2  Zhang San ", 38), ObjectClass3("obj3  Wang Meili ", 28)        )//  Randomly select the last object         val randomObj = objList.shuffled().last()        println(" The randomly generated object is ：$randomObj")//  If  it  The generated object is equal to T The type of , Will go as T  Straight back         return randomObj.takeIf { it is T } as T?   // null as T null as T?//  If  it  Randomly generated objects   It's not equal to  T type , Just go straight to the spare section below             ?: defaultLambdaAction()    }}

2、 Define extension functions

stay kotlin in , There are many extensible functions , Here are a few examples ：

    ObjectClass1(" Zhang San ", 22).show()    ObjectClass1("tiger", 22).getInfo()    println("tiger".addExtAction(3))//  Add extension function show()fun ObjectClass1.show(){    println(" I'm new show function ：name： $name, age：$age")}//  Add extension function getInfo()fun ObjectClass1.getInfo(){    println(" I'm new getInfo function ：name： $name, age：$age")}//  character string   Expand fun String.addExtAction(number: Int) = this + "@".repeat(number)data class ObjectClass1(val name: String, val age: Int)

3、 Nullable type function extension

    "tiger".outPutStringValue(" Pass on null  Just go here ")    null.outPutStringValue(" Pass on null  Just go here ")// String  When it cannot be empty , Can only pass values , In the case of nullable , It can be transmitted  null// defaultValue  Add an alternate function , The value passed in is  null  Under the circumstances , return  defaultValue  Alternate content fun String?.outPutStringValue(defaultValue: String){    println(this ?: defaultValue)}

4、infix keyword

infix Infix expression , It simplifies the code . Need to add Extension functions can only be used

//  Conditions for a ： For the first parameter  O1.test()  Function extension //  Condition 2 ： Need to be in   Brackets （o2: o2） In the parameters , Pass a parameter     "tiger".test("18")    "tiger" test ("18")    123 test ("18")// map  Comes with infix expressions     val mapOf = mapOf("tiger" to 2)    println(mapOf)infix fun <O1, O2> O1.test(o2: O2) {    println(" The content of the first parameter of infix expression is ：$this")    println(" The content of the second parameter of infix expression is ：$o2")}

5、 Transform function Map

//  principle ： Is to put   Anonymous functions   The return value of the last line , Add to a new collection , The generic type of the new set is R, And return the set     val listOf = listOf(" Zhang San ", " Wang Meili ", " It's beautiful ")    val map = listOf.map {        "[$it]"    }.map {        " What do you give , I dare to add  $it"    }    println(map)

6、 Transform function flatMap

//  principle ： Is to put   Anonymous functions   The return value of the last line , Add to a new collection , The generic type of the new set is R, And return the set     val listOf = listOf(" Zhang San ", " Wang Meili ", " It's beautiful ")             val map = listOf.map {        "[$it]"          //  One at a time string     }.flatMap {        listOf("$it  What do you give = I dare to add ","$it  To express dissatisfaction with ","$it  I think Wang is beautiful and ugly ")    //  Return one set at a time     }    println(map)

7、filter Filter function

// filter  The function is very simple to use ,  But it has to be a collection     val listOf1 = listOf(" Zhang San ", " Wang Meili ", " It's beautiful ")    val listOf2 = listOf(" Zhang s", " Liu Fang ", " Wang Wu ")    val ls2 = listOf(listOf1, listOf2)    val map = ls2.flatMap { it ->        it.filter {           it.contains(' Zhang ')        }    }//  The output is an array , The elements are only   contain  contains(' Zhang ')  Of     println(map)

8、 Merge operators

//  principle ： Is to put a collection   and   The second set   combined , Create a new collection ,  And back to //  Create a new collection （ Elements , Elements , Elements ）  Elements Pair(K, V)  Instead of the first set element  V Replace the elements of the second set     val listOf1 = listOf(" Zhang San ", " Wang Meili ", " It's beautiful ")    val listOf2 = listOf(45, 18, 21)    val zip = listOf1.zip(listOf2)    println(zip)//  Traverse     zip.forEach {        println(" Name is ：${it.first}  Age is ：${it.second}")    }    zip.toMap().forEach{        k, v ->        println(" Name is ：${k}  Age is ：${v}")    }

9、 Add kotlin Implementation of single case

//kotlin  Implementation of the singleton pattern class KotlinInstance private constructor() {    companion object {        val instance: KotlinInstance by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {            KotlinInstance()        }    }    fun show(){        println("show")    }}

summary

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