Kotlin教程：Map接口13个示例

Kotlin Map是一个接口和通用的元素集合。 Map接口以键和值对的形式保存数据。 映射的键是唯一的，每个键只保留一个值。 键和值可以是不同类型的对，例如<Int，Int>，<Int，String>，<Char，String>等。 此接口是不可变的，它的大小固定，方法支持只读访问。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

要使用Map接口，需要使用mapOf()或mapOf <k，v>()函数。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Map接口声明文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

interface Map<K, out V> (source)

Map接口的属性

Map接口函数

Map接口中有一些非常好用的函数，Map接口的函数如下所述。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Map接口示例1

下面使用mapOf <k，v>()函数声明和遍历Map值的示例。 在这个例子中，创建Int类型的键和String类型的值。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

fun main(args: Array<String>){

    val myMap = mapOf<Int,String>(1 to "Java", 4 to "Kotlin", 3 to "Python")
    for(key in myMap.keys){
        println(key.toString() +" => "+myMap[key])
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

1 => Java
4 => Kotlin
3 => Python

Map接口示例2 - 泛型

更具体地说，可以提供泛型类型Map，例如myMap：Map <k，v> = mapOf <k，v>()。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

fun main(args: Array<String>){

    val myMap: Map<Int, String> = mapOf<Int,String>(1 to "Maxsu", 4 to "Kotlin", 3 to "Java")
    for(key in myMap.keys){
        println("Element at key $key => ${myMap.get(key)}")
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 => Maxsu
Element at key 4 => Kotlin
Element at key 3 => Java

Map接口示例3 - 非泛型

如果不能指定Map接口的任何类型的键和值，那么它可以采用不同类型的键和值。 这是因为所有类内部都使用<Any，Any>类型。 例如：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

fun main(args: Array<String>){

    val myMap = mapOf(1 to "Java", 4 to "Python", 3 to "PHP","one" to "Yiibai", "two" to 2)
    for(key in myMap.keys){
        println("Element at key: '$key' => ${myMap.get(key)}")
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key: '1' => Java
Element at key: '4' => Python
Element at key: '3' => PHP
Element at key: 'one' => Yiibai
Element at key: 'two' => 2

Map接口示例4 - mapOf().getValue()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Java", 4 to "Kotlin", 3 to "Python")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }
    println(".....myMap.getValue(4).......")
    println(myMap.getValue(4))
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Java
Element at key 4 = Kotlin
Element at key 3 = Python
.....myMap.getValue(4).......
Kotlin

Map接口示例5 - mapOf().contains()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Yiibai", 4 to "Java", 3 to "Kotlin")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }

    println(".....myMap.contains(3).......")
    println( myMap.contains(3))
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Yiibai
Element at key 4 = Java
Element at key 3 = Kotlin
.....myMap.contains(3).......
true

Map接口示例6 - mapOf().containsKey()

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Yiibai", 4 to "Python", 3 to "Kotlin")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }

    println("......myMap.containsKey(2)......")
    println(myMap.containsKey(2))
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Yiibai
Element at key 4 = Python
Element at key 3 = Kotlin
......myMap.containsKey(2)......
false

Map接口示例7 - mapOf().containsValue()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Susen", 3 to "Python")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }
    println("......myMap.containsValue(\"Susen\")......")
    println(myMap.containsValue("Susen"))
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Maxsu
Element at key 4 = Susen
Element at key 3 = Python
......myMap.containsValue("Susen")......
true

Map接口示例8 - mapOf().get()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Python", 3 to "Susen")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }
    println(".....myMap.get(1).......")
    println(myMap.get(1))
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Maxsu
Element at key 4 = Python
Element at key 3 = Susen
.....myMap.get(1).......
Maxsu

Map接口示例9 - mapOf().getOrDefault()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Susen", 3 to "Python")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }

    println("......myMap.getOrDefault(3, \"Python\")......")
    println(myMap.getOrDefault(36, "Python3"))
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Maxsu
Element at key 4 = Susen
Element at key 3 = Python
......myMap.getOrDefault(3, "Python")......
Python3

Map接口示例10 - mapOf().asIterable ()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Susen", 3 to "Python")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }
    println(".......myMap.asIterable().....")
    for(itr in myMap.asIterable()){
        println("key = ${itr.key} value = ${itr.value}")
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Maxsu
Element at key 4 = Susen
Element at key 3 = Python
.......myMap.asIterable().....
key = 1 value = Maxsu
key = 4 value = Susen
key = 3 value = Python

Map接口示例11 - mapOf().iterator ()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Susen", 3 to "Python")

    for(key in myMap.keys){
        println("Element at：key $key => ${myMap.get(key)}")
    }
    println("......myMap.iterator()......")
    for(itr1 in myMap.iterator()){
        println("key = ${itr1.key}, value = ${itr1.value}")
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at：key 1 => Maxsu
Element at：key 4 => Susen
Element at：key 3 => Python
......myMap.iterator()......
key = 1, value = Maxsu
key = 4, value = Susen
key = 3, value = Python

Map接口示例12 - mapOf().minus()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Susen", 3 to "Python")

    for(key in myMap.keys){
        println("Element at key：$key => ${myMap.get(key)}")
    }
    println("......myMap.minus(4)......")
    for(m in myMap.minus(4)){
        println(myMap[m.key])
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key：1 => Maxsu
Element at key：4 => Susen
Element at key：3 => Python
......myMap.minus(4)......
Maxsu
Python

Map接口示例13 - mapOf().plus()函数

fun main(args: Array<String>){

    val myMap: Map<Int,String> = mapOf<Int, String>(1 to "Maxsu", 4 to "Susen", 3 to "Python")

    for(key in myMap.keys){
        println("Element at key $key = ${myMap.get(key)}")
    }
    println("......myMap.plus(Pair(5, \"Swift\"))......")
    for(p in myMap.plus(Pair(5, "Swift"))){
        println("Element at key ${p.key} = ${p.value}")
    }
}

执行上面示例代码，得到以下结果 -文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/18285.html

Element at key 1 = Maxsu
Element at key 4 = Susen
Element at key 3 = Python
......myMap.plus(Pair(5, "Swift"))......
Element at key 1 = Maxsu
Element at key 4 = Susen
Element at key 3 = Python
Element at key 5 = Swift

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