Kotlin - mutableMapOf()

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Kotlin MutableMap是集合框架的接口，该集合以键和值对的形式保存对象。 MutableMap接口的值通过使用其对应的键来检索。键和值可以是不同的对，例如<Int，Int>，<Int，String>，<Char，String>等。MutableMap的每个键仅包含一个值。

要使用MutableMap接口，无涯教程需要使用其名为mutableMapOf() 或mutableMapOf<k，v>()的函数。

MutableMap声明

interface MutableMap<K, V> : Map<K, V> (source)

MutableMap属性

PropertiesDescription
abstract val entries: MutableSet<MutableEntry<K, V>>这将返回映射中所有键和值对的MutableSet。
abstract val keys: MutableSet<K>这将返回此映射中MutableSet的所有键。
abstract val values: MutableCollection<V>这将返回当前映射中MutableCollection的所有值。此集合可能包含重复的值。

示例1: 遍历MutableMap

让无涯教程创建一个示例，使用mutablemapOf()函数创建一个MutableMap并遍历它。在此示例中，无涯教程以不同的方式创建了MutableMap的三种不同类型(MutableMap <Int，String>，MutableMap <String，String>和MutableMap <Any，Any>)。

复制代码
fun main(args: Array<String>) {

    val mutableMap1: MutableMap<Int, String> = mutableMapOf<Int, String>(1 to "Ashu", 4 to "Rohan", 2 to "Ajeet", 3 to "Vijay")

    val mutableMap2: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap2.put("name", "Ashu")
    mutableMap2.put("city", "Delhi")
    mutableMap2.put("department", "Development")
    mutableMap2.put("Learnfk", "Playing")
    val mutableMap3: MutableMap<Any, Any> = mutableMapOf<Any, Any>(1 to "Ashu", "name" to "Rohsan", 2 to 200)
    println(".....traverse mutableMap1........")
    for (key in mutableMap1.keys) {
        println("Key = ${key}, Value = ${mutableMap1[key]}")
    }
    println("......traverse mutableMap2.......")
    for (key in mutableMap2.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap2[key])
    }
    println("......traverse mutableMap3......")
    for (key in mutableMap3.keys) {
        println("Key = ${key}, Value = ${mutableMap3[key]}")
    }
}

输出:

.....traverse mutableMap1........
Key = 1, Value = Ashu
Key = 4, Value = Rohan
Key = 2, Value = Ajeet
Key = 3, Value = Vijay
......traverse mutableMap2.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
......traverse mutableMap3......
Key = 1, Value = Ashu
Key = name, Value = Rohsan
Key = 2, Value = 200

示例 - 2 put()和 putAll()

函数put()和putAll()用于在MutableMap中添加元素。 put()函数一次添加单个元素，而putAll()函数在MutableMap中添加集合类型元素。

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")


    val hashMap: HashMap<String,String> = hashMapOf<String,String>()
    hashMap.put("department", "Development")
    hashMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")
    for (key in mutableMap.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap[key])
    }
    mutableMap.putAll(hashMap)
    println("......traverse mutableMap after mutableMap.putAll(hashMap).......")
    for (key in mutableMap.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap[key])
    }
}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
......traverse mutableMap after mutableMap.putAll(hashMap).......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing

示例 - 3 containsKey()

containsKey()函数用于检查指定的键是否在MutableMap中存在。如果包含指定的键，则返回true，否则返回false。例如:

无涯教程网

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap[key])
    }

    println("......mutableMap.containsKey(\"city\").......")
    println(mutableMap.containsKey("city"))
}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
......mutableMap.containsKey("city").......
true

示例 - 4 containsValue()

containsValue()函数用于检查指定的值是否存在于MutableMap中。如果映射映射给定值的一个或多个键，则此函数返回true，否则返回false。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap[key])
    }

     println(".......mutableMap.containsValue(\"Delhi\")......")
     println(mutableMap.containsValue("Delhi"))
    println(".......mutableMap.containsValue(\"Mumbai\")......")
    println(mutableMap.containsValue("Mumbai"))
}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
.......mutableMap.containsValue("Delhi")......
true
.......mutableMap.containsValue("Mumbai")......
false

示例 - 5  contains()

contains()函数用于检查MutableMap中是否存在指定的键值。如果MutableMap中存在指定的键或值，则它将返回true，否则将返回false。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap[key])
    }

     println("......mutableMap.contains(\"city\").......")
     println(mutableMap.contains("city"))

}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
......mutableMap.contains("city").......
true

示例 - 6  get(key)

get(key)函数用于在MutableMap中检索指定键的对应值。如果MutableMap中不存在这样的键，则它返回null。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
        println("Key = "+key +", "+"Value = "+mutableMap[key])
    }

    println(".......mutableMap.get(\"department\")......")
    println(mutableMap.get("department"))

}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
.......mutableMap.get("department")......
Development

示例 - 7 getValue(key)

用于返回MutableMap的指定键的对应值的getValue()函数，或者如果在地图中找不到键，则抛出异常。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
         println("Key = ${key}, Value = ${mutableMap[key]}")
    }

    println(".......mutableMap.getValue(\"department\")......")
    println(mutableMap.getValue("department"))

}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
.......mutableMap.getValue("department")......
Development

示例 - 8 getOrDefault()

getOrDefault()函数返回MutableMap的指定键的对应值。如果MutableMap中不存在此类键，则它将返回默认提及值。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
       println("Key = ${key}, Value = ${mutableMap[key]}")
    }

    println(".......mutableMap.getOrDefault(\"name\", \"Default Value\")......")
    println(mutableMap.getOrDefault("name", "default value"))
}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
.......mutableMap.getOrDefault("name", "Default Value")......
Ashu

示例 - 9 count()

count()函数用于返回MutableMap中存在的元素总数。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
       println("Key = ${key}, Value = ${mutableMap[key]}")
    }

    println(".....mutableMap.count()........")
    println(mutableMap.count())
}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
.....mutableMap.count()........
4

示例 - 10 remove(key) and remove(key, value)

remove(key)函数用于删除与其提及键相对应的值。而remove(key，value)函数将删除包含key和value的元素。如果remove(key，value)函数将指定的键及其值一起移除，则返回true，否则返回false。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
       println("Key = ${key}, Value = ${mutableMap[key]}")
    }

    println("......mutableMap.remove(\"city\").......")
    println(mutableMap.remove("city"))

    println(".......mutableMap.remove(\"Learnfk\",\"Playing\")......")
    println(mutableMap.remove("Learnfk","Playing"))

    println("......traverse mutableMap.......")
    for (key in mutableMap.keys) {
        println("Key = ${key}, Value = ${mutableMap[key]}")
    }

}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
......mutableMap.remove("city").......
Delhi
.......mutableMap.remove("Learnfk","Playing")......
true
......traverse mutableMap after remove.......
Key = name, Value = Ashu
Key = department, Value = Development

示例 - 11 clear()

clear()函数用于从MutableMap中删除所有元素。例如:

复制代码
fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Ashu")
    mutableMap.put("city", "Delhi")
    mutableMap.put("department", "Development")
    mutableMap.put("Learnfk", "Playing")

    println("......traverse mutableMap.......")

   for (key in mutableMap.keys) {
       println("Key = ${key}, Value = ${mutableMap[key]}")
    }

    println("......mutableMap.clear().......")
    println(mutableMap.clear())
    println(mutableMap)
}

输出:

......traverse mutableMap.......
Key = name, Value = Ashu
Key = city, Value = Delhi
Key = department, Value = Development
Key = Learnfk, Value = Playing
......mutableMap.clear().......
kotlin.Unit
{}

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