Kotlin HashMap類

Kotlin HashMap是基於MutableMap介面的集合類。 Kotlin HashMap類使用Hash表實現MutableMap介面。 它以鍵和值對的形式存儲數據。 它表示為HashMap <key，value>或HashMap <K，V>。

HashMap類的實現不保證鍵，值和集合資料項目目的順序。

Kotlin HashMap類的構造函數

Kotlin HashMap類函數

Kotlin HashMap示例1 - 空HashMap

下麵是使用<Int，String>的空HashMap創建一個簡單的HashMap類定義示例，之後再添加元素。可使用HashMap [key]或HashMap.get(key)列印HashMap的值。

fun main(args: Array<String>){

    val hashMap:HashMap<Int,String> = HashMap<Int,String>() //define empty hashmap
    hashMap.put(1,"Java")
    hashMap.put(3,"SEO")
    hashMap.put(4,"Python")
    hashMap.put(2,"Kotlin")
    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key $key = ${hashMap[key]}")
    }
}

執行上面示例代碼，得到以下結果 -

.....traversing hashmap.......
Element at key 1 = Java
Element at key 2 = Kotlin
Element at key 3 = SEO
Element at key 4 = Python

Kotlin HashMap示例2- HashMap初始容量

HashMap也可以使用初始容量進行初始化。 可以通過添加和替換元素來更改容量。

fun main(args: Array<String>){

    val hashMap:HashMap<String,String> = HashMap<String,String>(3)
    hashMap.put("name","Maxsu")
    hashMap.put("city","海口")
    hashMap.put("department","技術部")
    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key: $key => ${hashMap[key]}")
    }
    println(".....hashMap.size.......")
    println(hashMap.size)
    hashMap.put("hobby","Travelling")
    println(".....hashMap.size  after adding hobby.......")
    println(hashMap.size)
    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key: $key => ${hashMap.get(key)}")
    }
}

執行上面示例代碼，得到以下結果 -

.....traversing hashmap.......
Element at key: name => Maxsu
Element at key: department => 技術部
Element at key: city => 海口
.....hashMap.size.......
3
.....hashMap.size  after adding hobby.......
4
.....traversing hashmap.......
Element at key: name => Maxsu
Element at key: department => 技術部
Element at key: city => 海口
Element at key: hobby => Travelling

Kotlin HashMap示例3- remove()和put()函數

remove()函數用於將指定鍵的現有值替換為指定值。 put()函數在指定鍵處添加新值並替換舊值。 如果put()函數沒有找到指定的鍵，它會在指定的鍵上放置一個新值。

fun main(args: Array<String>){

    val hashMap:HashMap<Int,String> = HashMap<Int,String>()
    hashMap.put(1,"Python")
    hashMap.put(3,"Java")
    hashMap.put(4,"Kotlin")
    hashMap.put(2,"Ruby")

    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key: $key => ${hashMap[key]}")
    }

    hashMap.replace(3,"Susen")
    hashMap.put(2,"Maxsu")
    println(".....hashMap.replace(3,"Susen")... hashMap.replace(2,"Maxsu")........")
    for(key in hashMap.keys){
        println("Element at key: $key => ${hashMap[key]}")
    }
}

執行上面示例代碼，得到以下結果 -

.....traversing hashmap.......
Element at key: 1 => Python
Element at key: 2 => Ruby
Element at key: 3 => Java
Element at key: 4 => Kotlin
.....hashMap.replace(3,"Susen")... hashMap.replace(2,"Maxsu")........
Element at key: 1 => Python
Element at key: 2 => Maxsu
Element at key: 3 => Susen
Element at key: 4 => Kotlin

Kotlin HashMap示例4 - containsKey(key)和containsValue(value)函數

如果指定的鍵在HashMap中存在，則containsKey()函數返回true;如果不存在此鍵，則返回false。

containsValue()函數用於檢查HashMap中是否存在指定的值。 如果HashMap中存在指定值，則返回true，否則返回false。

fun main(args: Array<String>){

    val hashMap:HashMap<Int,String> = HashMap<Int,String>()
    hashMap.put(1,"Ruby")
    hashMap.put(3,"Kotlin")
    hashMap.put(4,"Java")
    hashMap.put(2,"Python")

    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key: $key => ${hashMap[key]}")
    }

    println(".....hashMap.containsKey(3).......")
    println(hashMap.containsKey(3))
    println(".....hashMap.containsValue("Swift").......")
    println(hashMap.containsValue("Swift"))
}

執行上面示例代碼，得到以下結果 -

.....traversing hashmap.......
Element at key: 1 => Ruby
Element at key: 2 => Python
Element at key: 3 => Kotlin
Element at key: 4 => Java
.....hashMap.containsKey(3).......
true
.....hashMap.containsValue("Swift").......
false

Kotlin HashMap示例5 - clear()函數

clear()函數用於清除HashMap中的所有數據。如下示例 -

fun main(args: Array<String>){

    val hashMap:HashMap<Int,String> = HashMap<Int,String>()
    hashMap.put(1,"Java")
    hashMap.put(3,"Python")
    hashMap.put(4,"Kotlin")
    hashMap.put(2,"Ruby")

    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key: $key => ${hashMap[key]}")
    }

    println(".....hashMap.clear().......")
    hashMap.clear()
    println(".....print hashMap after clear().......")
    println(hashMap)
}

執行上面示例代碼，得到以下結果 -

.....traversing hashmap.......
Element at key: 1 => Java
Element at key: 2 => Ruby
Element at key: 3 => Python
Element at key: 4 => Kotlin
.....hashMap.clear().......
.....print hashMap after clear().......
{}