Kotlin基本语法3集合

1.List集合 

 1.1 只读List fun main() { val list = listOf("Jason", "Jack", "Jacky") println(list.getOrElse(3){"Unknown"}) println(list.getOrNull(3)?:"Unknown") }  1.2 可变List

fun main() { val mutableList = mutableListOf("Jason", "Jack", "Jacky") mutableList.add("Jimmy") mutableList.remove("Jack") mutableList.forEach(::println) val toList = mutableList.toList() println(toList===mutableList) }

 

1.2.mutator函数

fun main() { val mutableList = mutableListOf("Jason", "Jack", "Jacky") mutableList += "Jimmy" mutableList -= "Jason" mutableList.removeIf{it.contains("Jack")} println(mutableList) }  1.3. 遍历元素 fun main() { val list = listOf("Jason", "Jack", "Jacky") for (s in list) { println(s) } list.forEach{ println(it) } list.forEachIndexed { index, s -> println("$index $s") } }

 1.4 解构语法过滤元素

fun main() { val list = listOf("Jason", "Jack", "Jacky") val(zeroIndexEnum,_,twoIndexEnum)=list println(zeroIndexEnum) println(twoIndexEnum) } 2. Set 2.1 只读Set

 

fun main() { val set = setOf("Jason", "Jack", "Jacky", "Jack") val elementAt = set.elementAt(2) //这里用这个方法取下表 val elementAtOrNull = set.elementAtOrNull(5)//这个方法下表越界了，不会抛异常而是给null println(elementAt) } 2.2 可变Set集合 

fun main() { val set = mutableSetOf("Jason", "Jack", "Jacky", "Jack") set+="Jimmy" println(set) }  2.3 集合转换与快捷函数 fun main() { val set = mutableSetOf("Jason", "Jack", "Jacky", "Jack") set+="Jimmy" println(set) val listOf = listOf("Jason", "Jack", "Jacky", "Jack") val toList = listOf.toSet().toList()//不是一个对象了 val distinct = listOf.distinct()//不会修改原集合 println(listOf) println(distinct) } 3.数组类型

 

import java.io.File fun main() { val intArray:IntArray = intArrayOf(10, 20, 30) val toIntArray:IntArray = listOf(10, 20, 30).toIntArray() val array:Array<File> = arrayOf(File("xx"), File("xx")) } 4.Map  4.1 Map的创建

fun main() { val map:Map<String,Int> = mapOf("Jack" to 20, "Jason" to 18, "Jack" to 30) mapOf(Pair("Jimmy",20),Pair("Jason",16)) } 4.2 读取Map的值

fun main() { val map:Map<String,Int> = mapOf("Jack" to 20, "Jason" to 18, "Jack" to 30) println(map["Jack"]) println(map.getValue("Jack")) println(map.getOrElse("Rose"){"Unknown"}) println(map.getOrDefault("Rose",0)) }

 

4.3 Map的遍历

fun main() { val map:Map<String,Int> = mapOf("Jack" to 20, "Jason" to 18, "Jacky" to 30) map.forEach{ println("${it.key}, ${it.value}") } map.forEach { (key: String, value: Int) -> println("$key $value") } }  4.4 可变Map集合

fun main() { val map:MutableMap<String,Int> = mutableMapOf("Jack" to 20, "Jason" to 18, "Jacky" to 30) map += "Jimmy" to 30 map.put("Ji",3) val orPut = map.getOrPut("Rose") { 18 }//如果没有就添加进去 println(map) }