【Kotlin】List、Map、Set、Array 簡單比較與使用方式

簡單比較

• List : 有序、可重複
• Map : 鍵值對
• Set : 無序、不可重複
• Array : 有序、可重複、固定空間大小

List

fun main() {
    val numbers = listOf(0, 3, 8, 4, 0, 5, 5, 8, 9, 2)
    println("list:   ${numbers} numbers[4]=${numbers[4]}")
    println("sorted: ${numbers.sorted()}")
}

list:   [0, 3, 8, 4, 0, 5, 5, 8, 9, 2] numbers[4]=0
sorted: [0, 0, 2, 3, 4, 5, 5, 8, 8, 9]

Map

fun main() {
    val peopleAges = mutableMapOf(
        "Fred" to 30,
        "Ann" to 23
    )
    println(peopleAges)
    
    peopleAges.put("Barbara", 42)
    peopleAges["Joe"] = 51
    println(peopleAges)
    
    peopleAges["Fred"] = 31
    println(peopleAges)
    
    println("---")
    peopleAges.forEach { print("${it.key} is ${it.value}, ") }
    println()
    println(peopleAges.map { "${it.key} is ${it.value}" }.joinToString(", ") )

    println("---")
    val filteredNames = peopleAges.filter { it.key.length < 4 }
	println(filteredNames)
}

{Fred=30, Ann=23}
{Fred=30, Ann=23, Barbara=42, Joe=51}
{Fred=31, Ann=23, Barbara=42, Joe=51}
---
Fred is 31, Ann is 23, Barbara is 42, Joe is 51, 
Fred is 31, Ann is 23, Barbara is 42, Joe is 51
---
{Ann=23, Joe=51}

Set

fun main() {
    val numbers = listOf(0, 3, 8, 4, 0, 5, 5, 8, 9, 2)
    val setOfNumbers = numbers.toSet()
	println("set:    ${setOfNumbers}")
    println("contains 7: ${setOfNumbers.contains(7)}")
    println("contains 1: ${setOfNumbers.contains(0)}")
    
    println("-------")
    
    val set1 = setOf(1,2,3) //不可變
	val set2 = mutableSetOf(3,2,1) //可變
    println("$set1 == $set2: ${set1 == set2}")
}

set:    [0, 3, 8, 4, 5, 9, 2]
contains 7: false
contains 1: true
-------
[1, 2, 3] == [3, 2, 1]: true

Array

以 IntArray 為例

參考 : IntArray vs Array in Kotlin (tutorialspoint.com)

fun main() {
    val array = IntArray(3)
    array[0] = 1
    println(array.joinToString())
    for(n in array) {
		println(n)
    }
    
    val array2 = Array(3){9}
    println(array2.joinToString())
}

1, 0, 0
1
0
0
9, 9, 9

其他參考資料

Kotlin 中的集合 (android.com)