Kotlin MutableMap 接口

2024年8月29日 | 阅读 8 分钟

Kotlin MutableMap 是集合框架的一个接口，它以键值对的形式保存对象。 MutableMap 接口的值是通过使用它们对应的键来检索的。键和值可以是不同的对，例如 <Int, Int>、<Int, String>、<Char, String> 等。 MutableMap 的每个键只保存一个值。

要使用 MutableMap 接口，我们需要使用其名为 mutableMapOf() 或 mutableMapOf <k,v>() 的函数。

Kotlin MutableMap 接口声明

MutableMap 的属性

性质	描述
abstract val entries: MutableSet<MutableEntry<K, V>>	这会返回地图中所有键值对的 MutableSet。
abstract val keys: MutableSet<K>	这会返回此地图中 MutableSet 的所有键。
abstract val values: MutableCollection<V>	这会返回当前地图中 MutableCollection 的所有值。此集合可能包含重复的值。

Kotlin MutableMap 的函数

函数	描述
abstract fun put(key: K, value: V): V?	它使用指定的键将给定的值添加到地图中。
abstract fun putAll(from: Map<out K, V>)	这会使用来自提到的地图的键/值对更新当前地图。
abstract fun remove(key: K): V?	它从地图中删除指定的键及其对应的值。
open fun remove(key: K, value: V): Boolean	仅当键值对存在于地图中时，它才会从地图中删除键值实体。
abstract fun clear()	此函数用于从地图中删除所有元素。
operator fun <K, V> Map<out K, V>.contains(key: K): Boolean	它检查地图中给定的键。
abstract fun containsKey(key: K): Boolean	如果地图包含指定的键，则返回 true。
fun <K> Map<out K, *>.containsKey(key: K): Boolean	如果地图包含指定的键，则返回 true。
abstract fun containsValue(value: V): Boolean	如果地图为给定的值映射一个或多个键，则返回 true。
fun <K, V> Map<K, V>.containsValue(value: V): Boolean	如果地图为给定的值映射一个或多个键，则返回 true。
fun <K, V> Map<out K, V>.count(): Int	它返回地图实体的总数
operator fun <K, V> Map<out K, V>.get(key: K): V?	它返回对应于提到的键的值，如果地图中未找到此类键，则返回 null。
fun <K, V> Map<out K, V>.getOrDefault( key: K, defaultValue: V ): V	它返回带有对应提到的键的值，如果地图中没有该键的此类映射，则返回默认值。
fun <K, V> Map<K, V>.getOrElse( key: K, defaultValue: () -> V ): V	它返回地图中提到的键的值，如果未找到给定键的此类条目，则返回默认值函数。
fun <K, V> Map<K, V>.getValue(key: K): V	它返回与给定键对应的值，或者如果地图中未找到任何键，则抛出异常。

Kotlin MutableMap 示例 - 1 遍历 MutableMap

让我们创建一个示例，使用 mutablemapOf() 函数创建一个 MutableMap 并遍历它。在此示例中，我们创建了三种不同类型的 MutableMap（MutableMap<Int, String>、MutableMap<String, String> 和 MutableMap<Any, Any>），并使用不同的方式。

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("hobby", "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 = hobby, Value = Playing
......traverse mutableMap3......
Key = 1, Value = Ashu
Key = name, Value = Rohsan
Key = 2, Value = 200

Kotlin MutableMap 示例 - 2 put() 和 putAll()

函数 put() 和 putAll() 用于将元素添加到 MutableMap 中。 put() 函数一次添加一个元素，而 putAll() 函数将集合类型的元素添加到 MutableMap 中。例如

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("hobby", "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 = hobby, Value = Playing

Kotlin MutableMap 示例 - 3 containsKey()

containsKey() 函数用于检查指定的键是否存在于 MutableMap 中。如果它包含指定的键，则返回 true，否则返回 false。例如

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("hobby", "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 = hobby, Value = Playing
......mutableMap.containsKey("city").......
true

Kotlin MutableMap 示例 - 4 containsValue()

containsValue() 函数用于检查指定的值是否存在于 MutableMap 中。如果地图为给定的值映射一个或多个键，则此函数返回 true，否则返回 false。例如

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("hobby", "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 = hobby, Value = Playing
.......mutableMap.containsValue("Delhi")......
true
.......mutableMap.containsValue("Mumbai")......
false

Kotlin MutableMap 示例 - 5 contains()

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

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("hobby", "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 = hobby, Value = Playing
......mutableMap.contains("city").......
true

Kotlin MutableMap 示例 - 6 get(key)

get(key) 函数用于检索 MutableMap 中指定键的对应值。如果 MutableMap 中不存在此类键，则返回 null。例如

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("hobby", "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 = hobby, Value = Playing
.......mutableMap.get("department")......
Development

Kotlin MutableMap 示例 - 7 getValue(key)

getValue() 函数用于返回 MutableMap 的指定键的对应值，如果地图中未找到任何键，则抛出异常。例如

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("hobby", "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 = hobby, Value = Playing
.......mutableMap.getValue("department")......
Development

Kotlin MutableMap 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，则返回默认值。例如

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("hobby", "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 = hobby, Value = Playing
.......mutableMap.getOrDefault("name", "Default Value")......
Ashu

Kotlin MutableMap 示例 - 9 count()

count() 函数用于返回 MutableMap 中存在的元素总数。例如

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("hobby", "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 = hobby, Value = Playing
.....mutableMap.count()........
4

Kotlin MutableMap 示例 - 10 remove(key) 和 remove(key, value)

remove(key) 函数用于删除与其提到的键对应的值。而 remove(key, value) 函数删除包含键和值的元素。 remove(key, value) 函数在删除指定的键及其值时返回 true，否则返回 false。例如

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

Kotlin MutableMap 示例 - 11 clear()

clear() 函数用于从 MutableMap 中删除所有元素。例如

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("hobby", "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 = hobby, Value = Playing
......mutableMap.clear().......
kotlin.Unit
{}

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