速记

某人整理的csdn的kotlin地址:https://www.cnblogs.com/Jetictors/tag/Kotlin/

for (i in 1..10)
for (i in 1 until 10)
for (i in 10 downTo 1 step 1)

var binaryMap = TreeMap()
binaryMap['A']="A"

for ((letter, binary) in binaryMap) { ... }

val list = arrayListOf(1,2,3,4)
for((index, element) in list.withIndex()) { ... }

val result = try {
Integer.parseInt(i)
} catch (e: NumberFormatException) {
null
}

val str = if (true) "true" else "false"

fun max3(a:Int, b:Int) = if(a > b) a else b

fun getMnemonic(color: Color) = when (color) {
Color.RED -> "RED"
Color.ORANGE -> "ORANGE"
Color.YELLOW -> "YELLOW"
Color.GREEN -> "GREEN"
Color.BLUE -> "BLUE"
Color.WHITE -> "WHITE"
}

fun getWarmth(color: Color) = when (color) {
Color.RED, Color.BLUE, Color.GREEN -> "Wram"
Color.ORANGE, Color.WHITE, Color.YELLOW -> "Colder"
}

fun fizzBuzz(i: Int) = when {
i % 3 == 0 -> "Pizz"
i % 5 == 0 -> "Buzz"
i % 15 ==0 -> "PizzBuzz"
else -> "$i"
}

interface Expr
class Num(val value: Int): Expr // 实现了接口

// 三重引号的字符串(正则表达式放在三重引号的字符串中，其中字符不需转义.而不是\.)
val regex = """(.+)/(.+).(.+)""".toRegex()
val matchResult = regex.matchEntire(path)
if (matchResult != null) {
val (dictory, filename, extension) = matchResult.destructured
println("lists: filename, $extension")
}

/*

• 可变属性setter设定为私有

• */
  class LengthCounter {
  var counter:Int = 0
  private set

  fun addWord(word: String) {
  counter += word.length
  }
  }

// data作为修饰符说明其已经实现了toString，equals，hashCode
data class Client2(val name:String, val postalCode: Int) {}

object Payroll {} // 单例 Java调用Payroll.INSTANCE.xxx
companion object Payroll {} // 静态对象 Java调用Payroll.Companion.xxx, 类似于静态类
// 伴生对象就是类似java中的static，允许类内有静态函数或变量的存在!
// object表示其是一个静态类，后不要再跟class了

# 单例
fun main(args: Array) {

    println(Utils.instance.name) // 此处instance已被作为类的静态对象调用
}


class Utils private constructor() {
    fun sayHello()
    {
        println("hello")
    }
    var name="张三"
    var age=20
    companion object {
        val instance by lazy { Utils() }
    }
    
}

with() apply {}
?. ?: as? !! let{ ... } lateinit
Any, Unit, Nothing(常用于异常作为返回值，表示其不会正常终止)

Collection(只读)
MutableCollections(读写)

arrayOf(数组)
数组遍历:

  Array(5) {"item-"+(1+it)}.forEachIndexed { index, s -> println("$TAG index:$index,content: $s") }

use
inline reified
fun ensureTrailingPeriod(seg: T) where T: CharSequence, T: Appendable { ... } #此处where声明其实现接口类型

out(协变), in(逆变)， (类型投影)
Lambda的调用.invoke()