Kotlin basic learning 16

Catalog

1.Kotlin Nullable type extension function of language

2.Kotlin Linguistic infix keyword

3.Kotlin Definition extension file of language

4.Kotlin Language rename extended learning

5.Kotlin Linguistic DSL Study

6.Kotlin The transformation function of language map

7.Kotlin The transformation function of language -flatmap

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1.Kotlin Nullable type extension function of language

// Yes  String？==  Nullable type   Function extension , And there are backup values 
fun String?.outputStringValueFun(defaultValue:String) = println(this ?: defaultValue)
fun String?.outputStringValueFunGet(defaultValue: String) = if(this == null) defaultValue else this
// TODO 118.Kotlin Nullable type extension function of language 
fun main(){
    val infoValue : String ?= null
    infoValue.outputStringValueFun(" I'm the default 1")
    val name = "Derry"
    name.outputStringValueFun(" I'm the default 2")
    println(infoValue.outputStringValueFunGet(" I'm the default 3"))
    println(name.outputStringValueFunGet(" I'm the default 4"))
}

2.Kotlin Linguistic infix keyword

private infix fun<C1,C2>C1.gogogo(c2:C2){
    println(" Our infix expression , The content of a parameter is ：$this")
    println(" Our infix expression , The content of the second parameter is ：$c2")
}
// TODO 118.Kotlin Linguistic infix keyword 
//infix ==  Infix expression   It simplifies the code 
fun main(){
    // Here we are map Built in infix expression 
    mapOf(" zero ".to(0))
    mapOf(" One " to 1)
    mapOf(" Two " to 2)
    mapOf(" 3、 ... and " to 3)
    // We wrote our own infix expression 
    123 gogogo ' male '
    "Bxb".gogogo('M')
    "Bxb2" gogogo 'M'
}

3.Kotlin Definition extension file of language

// Guide pack 
import com.bxb.s6.bxb.randomItemValue
import com.bxb.s6.bxb.randomItemValuePrintln
// TODO 120.Kotlin Definition extension file of language 
fun main(){
    val list : List<String> = listOf(" Zhang San "," Li Si "," Wang Wu ")
    val set:Set<Double> = setOf(15.6,456.5,784.6)
    // If you don't need to extend the file 
    println(list.shuffled().first())
    println(set.shuffled().first())
    // Use extension files 
    println(list.randomItemValue())
    println(set.randomItemValue())
    list.randomItemValuePrintln()
    set.randomItemValuePrintln()
}

4.Kotlin Language rename extended learning

// Guide pack 
import com.bxb.s6.bxb.randomItemValue as g
import com.bxb.s6.bxb.randomItemValuePrintln as f
// TODO 120.Kotlin Language rename extended learning 
fun main(){
    val list : List<String> = listOf(" Zhang San "," Li Si "," Wang Wu ")
    val set:Set<Double> = setOf(15.6,456.5,784.6)

    // Use extension files 
    println(list.g())
    println(set.g())
    list.f()
    set.f()
}

5.Kotlin Linguistic DSL Study

import java.io.File

class Context{
    val info = " I am Bxb"
    val name = "DDD"
    fun toast(str:String) = println("toast:$str")
}
inline fun Context.apply5(lambda:Context.(String) -> Unit):Context{
    lambda(info)
    return this
}
//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
inline fun File.applyFile(action:(String,String?) -> Unit) : File{
    setWritable(true)
    setReadable(true)
    action(name,readLines()[0])
    return this
}
// TODO 123.Kotlin Linguistic DSL Study 
fun main(){
    val context:Context = Context().apply5 {
        //it == String == " I am Bxb"
        println(" my it yes $it, my this yes ：$this")
        toast("success")
        toast(it)
        toast(name)
        true
    }.apply5 {  }.apply5 {  }.apply5 {  }
    println()
    println(" I always output Context In itself ："+context.info)
    println()
    val file:File = File("D:\\a.txt")
        .applyFile { fileName, data ->
            println(" Your file name is ：$fileName, The data in your file is ：$data")
            println(" Your file name is ：$fileName, The data in your file is ：$data")
            println(" Your file name is ：$fileName, The data in your file is ：$data")
        }.applyFile { a, b ->  }.applyFile { a, b ->  }
    println(" I always output File In itself ：${file.name}")
}

6.Kotlin The transformation function of language map

// TODO 124.Kotlin The transformation function of language map
fun main(){
    val list = listOf(" Zhang San "," Li Si "," Wang Wu ")
    // principle ： Is to take you   Anonymous functions   The return value of the last line   Add a new collection , The generic type of scheming and is R, And return a new set 
    val list2 : List<Int> = list.map {
        "[$it]"
        88
    }
    println(list2)
    // purpose ： and RxJava The idea of , As like as two peas 
    val list3 : List<String> = list.map {
        " Name is ：$it"
    }.map {
        "$it, The length of the text is ：${it.length}"
    }.map {
        "[$it]"
    }
    for (s in list3){
        print("$s ")
    }
    println()

    list.map {
        " Name is ：$it"
    }.map {
        "$it, The length of the text is ：${it.length}"
    }.map {
        "[$it]"
    }.map {
        print("$it ")
    }
}

7.Kotlin The transformation function of language -flatmap

// TODO 125.Kotlin The transformation function of language -flatmap
// TODO flatmap  amount to  List<List<String>>  A collection of collections , There are nested relationships 
fun main(){
    val list:List<String> = listOf(" Zhang San "," Li Si "," Wang Wu ")
    val newList :List<String> = list.map {
        " Your name is ：$it"
    }.map {
        "$it, The length of your text is ：${it.length}"
    }.flatMap {
        listOf("$it  I'm learning C++","$it  I'm learning Java","$it  I'm learning Kotlin")
    }
    println(newList)
    println()
    val newList2:List<String> = list.flatMap {
        listOf("$it  I'm learning C++","$it  I'm learning Java","$it  I'm learning Kotlin")
    }
    println(newList2)
}