Kotlin –如何循环地图

向右看齐 2023-02-15 05:07 34阅读 0赞

在Kotlin中，您可以通过以下方式循环`Map` ：

1. for循环

val items = HashMap<String, Int>()
    	items["A"] = 10
    	items["B"] = 20
    	
    	for ((k, v) in items) {
    		println("$k = $v")
    	}

2. forEach

items.forEach { 
    		k, v -> 
    			println("$k = $v")
    	}

## 1.对于循环 ##

循环映射并通过键或值对其进行过滤。

fun main(args: Array<String>) {
    
        val items = HashMap<String, Int>()
        items["A"] = 10
        items["B"] = 20
        items["C"] = 30
    
        println("-- Example 1 -- \n $items");
    
        //for loop
        println("\n-- Example 1.1 -- ");
        for ((k, v) in items) {
            println("$k = $v")
        }
    
        //for loop + lambdas filter
        println("\n-- Example 1.2 --");
        for ((k, v) in items) {
            if (k == "C")
                println("Find by key 'C' : $k = $v")
        }
    
        //Actually, you can filter key like this
        println("\n-- Example 1.3 -- ");
        val filteredItems = items.filterKeys { it == "A" || it == "C" }
        println("Find by key == A or C : $filteredItems")
    
        //Or filter value like this
        println("\n-- Example 1.4 --");
        val filterItems2 = items.filterValues { it <= 20 }
        println("Find by value <=20 : $filterItems2")
    
        //Or just filters
        println("\n-- Example 1.5 --");
        val filterItems3 = items.filter { it.key == "B" && it.value == 20 }
        println("Find by key == 'B' and value == 20 : $filterItems3")
    
    }

输出量

-- Example 1 -- 
     {A=10, B=20, C=30}
    
    -- Example 1.1 -- 
    A = 10
    B = 20
    C = 30
    
    -- Example 1.2 --
    Find by key 'C' : C = 30
    
    -- Example 1.3 -- 
    Find by key == A or C : {A=10, C=30}
    
    -- Example 1.4 --
    Find by value <=20 : {A=10, B=20}
    
    -- Example 1.5 --
    Find by key = 'B' and value ==20 : {B=20}

## 2. forEach ##

fun main(args: Array<String>) {
    
        val items2 = hashMapOf("A" to 10, "B" to 20, "C" to 30)
        items2["D"] = 40
    
        // foreach example
        println("\n-- Example 2.1 --");
        items2.forEach { k, v ->
            println("$k = $v")
        }
    
        // foreach + filter
        println("\n-- Example 2.1 --");
        items2.forEach { k, v ->
            if (v == 10) {
                println("$k = $v")
            }
        }
    
        // using the special 'it' like this
        println("\n-- Example 2.2 --");
        items2.forEach { println("key : ${it.key}, value : ${it.value}") }
    
    }

输出量

-- Example 2.1 --
    A = 10
    B = 20
    C = 30
    D = 40
    
    -- Example 2.1 --
    A = 10
    
    -- Example 2.2 --
    key : A, value : 10
    key : B, value : 20
    key : C, value : 30
    key : D, value : 40

## 参考文献 ##

1.  [Kotlin地图][Kotlin]
2.  [Kotlin过滤器按键][Kotlin 1]
3.  [Kotlin forEach][]

标签： [循环][Link 1] [foreach][] [Kotlin][Kotlin 2] [地图的][Link 2] [过滤器][Link 3]

> 翻译自: [https://mkyong.com/kotlin/kotlin-how-to-loop-a-map/][https_mkyong.com_kotlin_kotlin-how-to-loop-a-map]

[Kotlin]: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-map/index.html
[Kotlin 1]: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/filter-keys.html
[Kotlin forEach]: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/for-each.html
[Link 1]: https://mkyong.com/tag/for-loop/
[foreach]: https://mkyong.com/tag/foreach/
[Kotlin 2]: https://mkyong.com/tag/kotlin/
[Link 2]: https://mkyong.com/tag/map/
[Link 3]: https://mkyong.com/tag/filter/
[https_mkyong.com_kotlin_kotlin-how-to-loop-a-map]: https://mkyong.com/kotlin/kotlin-how-to-loop-a-map/