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list

創建和修改

不可變list,listOf

var list = listOf("a","d","f")
println(list.getOrElse(3){"Unknown"})
println(list.getOrNull(3) ?: "Unknown")

創建和修改可變list，mutableList

val mutableList = mutableListOf("a","d","f")
mutableList.removeIf { it.contains("a") }

遍歷和解構

forIn，forEach,forEachIndexed

用下劃線_來跳過不需要的元素

for (s in list){println(s)
}list.forEach{println(it)
}list.forEachIndexed { index, item ->println("$index, $item")
}
//解構
val(a,_,c) = list 

"_"表示跳過這個元素，跳過的元素不會被讀取

轉換

list.toMutableList()

去重

list.distinct()

快速篩選和排序

可以結合filter、forEach、sortedByDescending、sortedBy來快速對一個list進行篩選和排序

val resultList = mutableListOf<AppInfo>()
val recommendations = listOf(AppA(), AppB(), AppC())
//根據app的安裝時間按照倒序排列
recommendations.filter { //filter里跟篩選的條件，符合條件的數據會繼續走后面的排序it.isAppInstalled() 
}  
.sortedByDescending { //這里是排序的條件，sortedBy是正序it.getAppInstalledTime() 
}.forEach { resultList.add(it) }

set

不可重復的，去重里面的元素，函數操作基本同list

map

fun main() {val map = mapOf("Jack" to 20, "Jim" to 18)mapOf(Pair("Jim",20), Pair("json",30))println(map["Jack"])println(map.getValue("Jack"))println(map.getOrElse("java"){"unknown"})println(map.getOrDefault("java", 0))map.forEach{println("${it.key}, ${it.value}")}val mutableMap = mutableMapOf("Jack" to 20, "Jim" to 18)//添加元素mutableMap += "jim" to 30mutableMap["jim"] = 31mutableMap.getOrPut("role"){19}println(mutableMap)
}

to，實際上是一個函數，返回一個Pair結果

去重

val clone = filteredDirectories.clone() as ArrayList<Directory>
//數據去重。
callback(clone.distinctBy { it.path.getDistinctPath() } as ArrayList<Directory>)

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