集合有助于數據分組，方便后續操作

集合類型	說明
Lists	有序的可重復的集合
Sets	無序的不可重復的集合
Maps	鍵值對映射集合，鍵唯一，且一個鍵只能映射到一個值

每個集合類型都可以是可變的或者只讀的

List

List按照添加的順序存儲內容，并允許重復

存儲的內容通常稱作元素

List類型

創建只讀List使用listOf()方法

創建可變List使用mutableListOf()方法

在創建列表時，Kotlin可以推斷存儲項的類型。可以在列表聲明后的尖括號<>中添加類型來顯式聲明類型

fun main() {val readOnlyShapes = listOf("triangle", "square", "circle")println(readOnlyShapes) // [triangle, square, circle]val shapes: MutableList<String> = mutableListOf("triangle", "square", "circle")println(shapes) // [triangle, square, circle]shapes[2] = "circle2"// shapes[3] = "circle3"   // Index 3 out of bounds for length 3println(shapes) // [triangle, square, circle2]
}

操作MutableList索引不能超過初始長度

為了防止不必要的修改，你可以通過將可變列表賦值給List來獲得它們的只讀視圖

fun main() {val shapes: MutableList<String> = mutableListOf("triangle", "square", "circle")val shapesLocked: List<String> = shapes
}

這種方式通常叫做鑄造（casting）

List常用方法

查看List方法

獲取元素

fun main() {val readOnlyShapes = listOf("triangle", "square", "circle")println("The first item in the list is: ${readOnlyShapes[0]}")  // The first item in the list is: triangleprintln("The first item in the list is: ${readOnlyShapes.first()}") // The first item in the list is: triangleprintln("The last item in the list is: ${readOnlyShapes.last()}")   // The last item in the list is: circle
}

獲取長度

fun main() {val readOnlyShapes = listOf("triangle", "square", "circle")println("This list has ${readOnlyShapes.count()} items") // This list has 3 items
}   

判斷是否包含某一元素

fun main() {val readOnlyShapes = listOf("triangle", "square", "circle")println("circle" in readOnlyShapes) // true
}

新增和刪除

fun main() {val shapes: MutableList<String> = mutableListOf("triangle", "square", "circle")// 添加 "pentagon"shapes.add("pentagon")println(shapes) // [triangle, square, circle, pentagon]// 刪除第一個 "pentagon"shapes.remove("pentagon")println(shapes) // [triangle, square, circle]
}

Set

Set集合中存儲的數據無序并且不能重復

Set類型

創建只讀Set使用setOf()方法

創建可變Set使用MutableList()方法

fun main() {val readOnlyFruit = setOf("apple", "banana", "cherry", "cherry")val fruit: MutableSet<String> = mutableSetOf("apple", "banana", "cherry", "cherry")
}

Set常用方法

獲取元素

因為Set為無序集合，所以不能通過索引獲取集合元素

fun main() {val set = setOf("apple", "banana", "cherry", "cherry")println("The first item in the set is: ${set.first()}") // The first item in the set is: appleprintln("The last item in the set is: ${set.last()}") //  The last item in the set is: cherry
}

Map

Map以鍵值對的形式存儲數據。你可以通過引用鍵來訪問值

鍵是唯一的，如果插入重復鍵則會覆蓋之前的值

Map類型

要創建只讀Map，使用mapOf()函數
要創建可變地圖MutableMap，使用mutableMapOf()函數

在創建Map時，kotlin可以推斷出存儲的元素類型。要顯式聲明類型，可以在Map聲明后的尖括號<>中添加鍵和值的類型。例如：MutableMap<String, Int>。鍵的類型為String，值的類型為Int

fun main() {val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(readOnlyJuiceMenu)  // {apple=100, kiwi=190, orange=100}val juiceMenu: MutableMap<String, Int> = mutableMapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(juiceMenu)  // {apple=100, kiwi=190, orange=100}
}

常用方法

獲取數據

使用鍵獲取值

fun main() {val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(readOnlyJuiceMenu["apple"]) // 100
}

獲取所有的鍵或者值

fun main() {val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(readOnlyJuiceMenu.keys) // [apple, kiwi, orange]println(readOnlyJuiceMenu.values)   // [100, 190, 100]
}

獲取鍵值對數量

fun main() {val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(readOnlyJuiceMenu.count()) // 3
}

修改/刪除

fun main() {val juiceMenu: MutableMap<String, Int> = mutableMapOf("apple" to 100, "kiwi" to 190, "orange" to 100)juiceMenu.put("coconut", 150) // 添加鍵"coconut"和值 150println(juiceMenu) // {apple=100, kiwi=190, orange=100, coconut=150}juiceMenu.put("apple", 200) // 修改"coconut"的值成 200println(juiceMenu) // {apple=200, kiwi=190, orange=100, coconut=150}juiceMenu.remove("orange")    // 刪除"orange"println(juiceMenu)  // {apple=200, kiwi=190, coconut=150}
}

是否包含某元素

是否包含某個鍵

fun main() {val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(readOnlyJuiceMenu.containsKey("kiwi"))  // trueprintln("orange" in readOnlyJuiceMenu.keys) // true
}

是否包含某個值

fun main() {val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)println(200 in readOnlyJuiceMenu.values)  // false
}