Kotlin MutableMap接口

Kotlin MutableMap是集合框架的接口，它以鍵和值對的形式保存對象。 通過使用相應的鍵來檢索MutableMap接口的值。 鍵和值可以是不同類型的對，例如<Int，Int>，<Int，String>，<Char，String>等等。MutableMap的每個鍵只保存一個值。

要使用MutableMap接口，我們需要使用它的函數：mutableMapOf()或mutableMapOf <k,v>()。

Kotlin MutableMap接口聲明

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

MutableMap屬性

屬性

描述

MutableSet<MutableEntry<K, V>>

這將返回映射中所有鍵和值對的MutableSet。

MutableSet<K>

這將返回此映射中MutableSet的所有鍵。

MutableCollection<V>

這將返回當前映射中MutableCollection的所有值。 此集合可能包含重複值。

Kotlin MutableMap的函數

函數

描述

abstract fun put(key: K, value: V): V?

使用映射中的指定鍵添加給定值。

abstract fun putAll(from: Map<out K, V>)

使用指定映射中的鍵/值對更新當前映射。

abstract fun remove(key: K): V?

從映射中刪除指定的鍵及對應的值。

open fun remove(key: K, value: V): Boolean

僅當映射中存在鍵和值實體時，它纔會從映射中刪除它們。

abstract fun clear()

此函數用於從映射中刪除所有元素。

operator fun <K, V> Map<out K, V>.contains(key: K): Boolean

它檢查映射中是否包含給定鍵。

abstract fun containsKey(key: K): Boolean

如果map包含指定的鍵，則返回true。

fun <K> Map<out K, *>.containsKey(key: K): Boolean

如果map包含指定的鍵，則返回true。

abstract fun containsValue(value: V): Boolean

如果映射包含給定值的一個或多個鍵，則返回true。

fun <K, V> Map<K, V>.containsValue(value: V): Boolean

如果映射包含給定值的一個或多個鍵，則返回true。

fun <K, V> Map<out K, V>.count(): Int

它返回映射的項目總數。

operator fun <K, V> Map<out K, V>.get(key: K): V?

它返回與鍵對應的值，如果在映射中找不到指定鍵，則返回null。

fun <K, V> Map<out K, V>.getOrDefault(key: K, defaultValue: V): V

它返回帶有相應指定鍵的值，或者如果映射中沒有鍵的映射，則返回默認值。

fun <K, V> Map<K, V>.getOrElse(key: K, defaultValue: () -> V ): V

它返回映射中提及鍵的值，或者如果找不到給定鍵的此類條目，則返回默認值函數。

fun <K, V> Map<K, V>.getValue(key: K): V

它返回與給定鍵對應的值，如果在映射中找不到鍵，則拋出異常。

Kotlin MutableMap示例 - 1遍歷MutableMap

首先創建一個使用mutablemapOf()函數創建MutableMap並遍歷它的示例。 在這個例子中，使用不同的方式(MutableMap <Int，String>，MutableMap <String，String>和MutableMap <Any，Any>)來創建MutableMap的三種不同類型。

fun main(args: Array<String>) {

    val mutableMap1: MutableMap<Int, String> = mutableMapOf<Int, String>(1 to "Java", 4 to "Ruby", 2 to "Ajax", 3 to "Vivi")
    val mutableMap2: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap2.put("name", "Susen")
    mutableMap2.put("city", "海口")
    mutableMap2.put("department", "研發部")
    mutableMap2.put("hobby", "擼代碼")
    val mutableMap3: MutableMap<Any, Any> = mutableMapOf<Any, Any>(1 to "Maxsu", "name" to "Ruby", 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]}")
    }
}

執行上面示例代碼，得到以下結果 -

.....traverse mutableMap1........
Key = 1, Value = Java
Key = 4, Value = Ruby
Key = 2, Value = Ajax
Key = 3, Value = Vivi
......traverse mutableMap2.......
Key = name, Value = Susen
Key = city, Value = 海口
Key = department, Value = 研發部
Key = hobby, Value = 擼代碼
......traverse mutableMap3......
Key = 1, Value = Maxsu
Key = name, Value = Ruby
Key = 2, Value = 200

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

put()和putAll()函數用於添加MutableMap中的元素。put()函數向MutableMap中添加單個元素，putAll()函數向MutableMap添加集合類型元素。例如：

fun main(args: Array<String>) {

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

    val hashMap: HashMap<String,String> = hashMapOf<String,String>()
    hashMap.put("department", "研發部")
    hashMap.put("hobby", "擼代碼")

    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])
    }
}

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Susen
Key = city, Value = 海口
......traverse mutableMap after mutableMap.putAll(hashMap).......
Key = name, Value = Susen
Key = city, Value = 海口
Key = department, Value = 研發部
Key = hobby, Value = 擼代碼

Kotlin MutableMap示例3 - containsKey()函數

containsKey()函數用於檢查MutableMap中是否存在指定的鍵。 如果它包含指定的鍵，則返回true，否則返回false。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "研發部")
    mutableMap.put("hobby", "女")

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

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

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

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = 研發部
Key = hobby, Value = 女
......mutableMap.containsKey("city").......
true

Kotlin MutableMap示例4 - containsValue()函數

containsValue()函數用於檢查MutableMap中是否存在指定的值。 如果映射包含給定的一個或多個值，則此函數返回true，否則返回false。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "研發部")
    mutableMap.put("hobby", "擼代碼")

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

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

    println(".......mutableMap.containsValue(\"上海\")......")
    println(mutableMap.containsValue("上海"))
    println(".......mutableMap.containsValue(\"Maxsu\")......")
    println(mutableMap.containsValue("Maxsu"))
}

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = 研發部
Key = hobby, Value = 擼代碼
.......mutableMap.containsValue("上海")......
false
.......mutableMap.containsValue("Maxsu")......
true

Kotlin MutableMap示例5 - contains()函數

contains()函數用於檢查MutableMap中是否存在指定的值鍵。如果指定的鍵或值存在於MutableMap中，則它將返回true，否則返回false。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Susen")
    mutableMap.put("city", "Haikou")
    mutableMap.put("department", "Development")
    mutableMap.put("hobby", "Coding")

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

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

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

}

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Susen
Key = city, Value = Haikou
Key = department, Value = Development
Key = hobby, Value = Coding
......mutableMap.contains("city").......
true

Kotlin MutableMap示例6 - get(key)函數

get(key)函數用於檢索MutableMap中指定鍵的對應值。如果MutableMap中沒有包含指定鍵，則返回null。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Susen")
    mutableMap.put("city", "Haikou")
    mutableMap.put("department", "Development")
    mutableMap.put("hobby", "Coding")

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

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

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

}

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Susen
Key = city, Value = Haikou
Key = department, Value = Development
Key = hobby, Value = Coding
.......mutableMap.get("department")......
Development

Kotlin MutableMap示例7 - getValue(key)函數

getValue()函數用於返回MutableMap的指定鍵的相應值，如果在map中找不到鍵，則拋出異常。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "Development")
    mutableMap.put("hobby", "擼代碼")

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

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

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = Development
Key = hobby, Value = 擼代碼
.......mutableMap.getValue("department")......
Development

Kotlin MutableMap示例8 - getOrDefault()函數

getOrDefault()函數返回MutableMap指定鍵的對應值。 如果MutableMap中不存在指定的鍵，則返回默認對應值。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "Development")
    mutableMap.put("hobby", "擼代碼")

    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"))

}

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = Development
Key = hobby, Value = 擼代碼
.......mutableMap.getOrDefault("name", "Default Value")......
Maxsu

Kotlin MutableMap示例9 - count()函數

count()函數用於返回MutableMap中存在的元素總數。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "Development")
    mutableMap.put("hobby", "擼代碼")
    println("......traverse mutableMap.......")

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

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

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = Development
Key = hobby, Value = 擼代碼
.....mutableMap.count()........
4

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

remove(key)函數用於刪除與指定鍵對應的值。 而remove(key，value)函數刪除包含鍵和值的元素。 如果成功刪除指定的鍵及其值，則remove(key，value)函數返回true，否則返回false。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "Development")
    mutableMap.put("hobby", "擼代碼")
    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\",\"擼代碼\")......")
    println(mutableMap.remove("hobby","擼代碼"))

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

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = Development
Key = hobby, Value = 擼代碼
......mutableMap.remove("city").......
海口
.......mutableMap.remove("hobby","擼代碼")......
true
......traverse mutableMap.......
Key = name, Value = Maxsu
Key = department, Value = Development

Kotlin MutableMap示例11 - clear()函數

clear()函數用於從MutableMap中刪除所有元素。 例如：

fun main(args: Array<String>) {

    val mutableMap: MutableMap<String, String> = mutableMapOf<String, String>()
    mutableMap.put("name", "Maxsu")
    mutableMap.put("city", "海口")
    mutableMap.put("department", "技術部")
    mutableMap.put("hobby", "擼代碼")

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

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

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

執行上面示例代碼，得到以下結果 -

......traverse mutableMap.......
Key = name, Value = Maxsu
Key = city, Value = 海口
Key = department, Value = 技術部
Key = hobby, Value = 擼代碼
......mutableMap.clear().......
kotlin.Unit
{}