Kotlin MutableMap：mutableMapOf()

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📜 Kotlin MutableMap：mutableMapOf()

📅 最后修改于: 2021-01-05 07:49:57 🧑 作者: Mango

Kotlin MutableMap界面

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，，等。MutableMap的每个键仅包含一个值。

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

Kotlin MutableMap接口声明

interface MutableMap : Map (source)

MutableMap的属性

Properties	Description
abstract val entries: MutableSet>	This returns a MutableSet of all its key and value pairs in the map.
abstract val keys: MutableSet	This returns all the keys of MutableSet in this map.
abstract val values: MutableCollection	This returns all the values of MutableCollection in the current map. This collection may contain duplicate values.

Kotlin MutableMap的功能

Function	Description
abstract fun put(key: K, value: V): V?	It adds the given value with the specified key in the map.
abstract fun putAll(from: Map)	This updates the current map with key/value pairs from the mentioned map.
abstract fun remove(key: K): V?	It removes the specified key with its corresponding value from the map.
open fun remove(key: K, value: V): Boolean	It removes the key and value entities from the map only if it exist in the map.
abstract fun clear()	This function is used to removes all the elements from the map.
operator fun Map.contains(key: K): Boolean	It checks the given key in the map.
abstract fun containsKey(key: K): Boolean	It returns the true if map contains the specified key.
fun Map.containsKey(key: K): Boolean	It returns the true if map contains the specified key.
abstract fun containsValue(value: V): Boolean	It returns true if the map maps one or more keys for the given value.
fun Map.containsValue(value: V): Boolean	It returns true if the map maps one or more keys for the given value.
fun Map.count(): Int	It returns the total number of entities of the map
operator fun Map.get(key: K): V?	It returns the value corresponding to mention key, or null if no such key found in the map.
fun Map.getOrDefault( key: K, defaultValue: V ): V	It returns the value with corresponding mention key, or it returns default value if no such mapping for the key in the map.
fun Map.getOrElse( key: K, defaultValue: () -> V ): V	It returns the value for the mention key in the map, or it returns the default value function if no such entry found for the given key.
fun Map.getValue(key: K): V	It returns the value corresponding to given key, or it throws an exception if no key found in the map.

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，我们以不同的方式创建了MutableMap的三种不同类型(MutableMap ，MutableMap 和MutableMap )。

fun main(args: Array) {

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

    val mutableMap2: MutableMap = mutableMapOf()
    mutableMap2.put("name", "Ashu")
    mutableMap2.put("city", "Delhi")
    mutableMap2.put("department", "Development")
    mutableMap2.put("hobby", "Playing")
    val mutableMap3: MutableMap = mutableMapOf(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()用于在MutableMap中添加元素。 put()函数添加单个元素，而putAll()函数在MutableMap中添加集合类型元素。例如：

fun main(args: Array) {

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


    val hashMap: HashMap = hashMapOf()
    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在MutableMap中存在。如果包含指定的键，则返回true，否则返回false。例如：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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)函数用于在MutableMap中检索指定键的对应值。如果MutableMap中不存在此类键，则返回null。例如：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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)

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：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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，则它将返回默认提及值。例如：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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) {

    val mutableMap: MutableMap = mutableMapOf()
    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及键相对应的值。而remove(key，value)函数删除包含键和值的元素。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：

fun main(args: Array) {

    val mutableMap: MutableMap = mutableMapOf()
    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) {

    val mutableMap: MutableMap = mutableMapOf()
    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
{}