Kotlin Quick Start (f) higher-order functions and custom dsl

Preface: This part is the difference between java and unique, it is equivalent to the method you good package, you only need a simple line of code, you can complete java need a lot of lines of code work.

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Usage of high-level functions

Define a class and a set Girl

data class Girl(var name: String, var age: Int, var height: Int, var address: String)

var girlDB = listOf<Girl>(
    Girl("aa", 18, 180, "河南"),
    Girl("bb", 28, 180, "广西"),
    Girl("cc", 38, 180, "浙江"),
    Girl("dd", 48, 180, "北京"),
    Girl("ee", 28, 190, "河南"),
    Girl("ff", 28, 180, "广东")
)

The oldest data output

fun main(args: Array<String>) {
    println(girlDB.maxBy { it.age })
}

filter to filter the output

 println(girlDB.filter {
        (it.age<30) and (it.height>180) and (it.age>18)
    })

map output

 var result = girlDB.map {
        "${it.name} : ${it.age}"
    }
 println(result)

count output

    println(girlDB.count{
        it.age>18
    })

groupBy output

    var result = girlDB.groupBy {
        it.address
    }.get("河南")?.forEach{println(it)}
    println(result)

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Usage of custom dsl

In the method of adding the class Girl

infix fun List<Girl>.query(age:Int){
    filter {
        it.age <age
    }.forEach (::println)
}

Then call Main

fun main(args: Array<String>) {
    girlDB query 50
}

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Ok! End.