Android面试题之Kotlin常见集合操作技巧

本文首发于公众号“AntDream”，欢迎微信搜索“AntDream”或扫描文章底部二维码关注，和我一起每天进步一点点

list

创建和修改

不可变list,listOf

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

创建和修改可变list，mutableList

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

遍历和解构

forIn，forEach,forEachIndexed

用下划线_来跳过不需要的元素

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

"_"表示跳过这个元素，跳过的元素不会被读取

转换

list.toMutableList()

去重

list.distinct()

快速筛选和排序

可以结合filter、forEach、sortedByDescending、sortedBy来快速对一个list进行筛选和排序

val resultList = mutableListOf<AppInfo>()
val recommendations = listOf(AppA(), AppB(), AppC())
//根据app的安装时间按照倒序排列
recommendations.filter { //filter里跟筛选的条件，符合条件的数据会继续走后面的排序it.isAppInstalled() 
}  
.sortedByDescending { //这里是排序的条件，sortedBy是正序it.getAppInstalledTime() 
}.forEach { resultList.add(it) }

set

不可重复的，去重里面的元素，函数操作基本同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，实际上是一个函数，返回一个Pair结果

去重

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

---

欢迎关注我的公众号查看更多精彩文章！