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📜  Kotlin HashMap

📅  最后修改于: 2021-01-05 07:47:19             🧑  作者: Mango

Kotlin HashMap类

Kotlin HashMap是基于MutableMap接口的集合类。 Kotlin HashMap类使用Hash表实现MutableMap接口。它以键和值对的形式存储数据。它表示为HashMap 或HashMap 。

HashMap类的实现不能保证键，值和集合条目的数据顺序。

Kotlin HashMap类的构造方法

Constructor Description
HashMap() It constructs an empty HashMap instance
HashMap(initialCapacity: Int, loadFactor: Float = 0f) It is used to constructs a HashMap of specified capacity.
HashMap(original: Map) It constructs a HashMap instance filled with contents of specified original map.

Kotlin HashMap类的功能

Functions Description
open fun put(key: K, value: V): V? It puts the specified key and value in the map
open operator fun get(key: K): V? It returns the value of specified key, or null if no such specified key is available in map.
open fun containsKey(key: K): Boolean It returns true if map contains specifies key.
open fun containsValue(value: V): Boolean It returns true if map maps one of more keys to specified value.
open fun clear() It removes all elements from map.
open fun remove(key: K): V? It removes the specified key and its corresponding value from map

Kotlin HashMap示例1-空HashMap

让我们创建一个简单的HashMap类定义示例，该类使用的空HashMap定义并稍后添加元素。要printHashMap的值，我们将使用HashMap [key]或HashMap.get(key) 。

fun main(args: Array){

    val hashMap:HashMap = HashMap() //define empty hashmap
    hashMap.put(1,"Ajay")
    hashMap.put(3,"Vijay")
    hashMap.put(4,"Praveen")
    hashMap.put(2,"Ajay")
    println(".....traversing hashmap.......")
    for(key in hashMap.keys){
        println("Element at key $key = ${hashMap[key]}")
    }}

输出：

.....traversing hashmap.......
Element at key 1 = Ajay
Element at key 2 = Ajay
Element at key 3 = Vijay
Element at key 4 = Praveen

Kotlin HashMap示例2- HashMap的初始容量

HashMap也可以使用其初始容量进行初始化。可以通过添加和替换其元素来更改容量。

fun main(args: Array){

    val hashMap:HashMap = HashMap(3)
    hashMap.put("name","Ajay")
    hashMap.put("city","Delhi")
    hashMap.put("department","Software Development")
    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)}")
    }
}

输出：

.....traversing hashmap.......
Element at key name = Ajay
Element at key department = Software Development
Element at key city = Delhi
.....hashMap.size.......
3
.....hashMap.size  after adding hobby.......
4
.....traversing hashmap.......
Element at key name = Ajay
Element at key department = Software Development
Element at key city = Delhi
Element at key hobby = Travelling

Kotlin HashMap示例3- remove()和put()

函数remove()用于将指定键处的现有值替换为指定值。 put()函数在指定的键处添加一个新值，并替换旧值。如果put()函数未找到任何指定的键，它将在指定的键处放置一个新值。

fun main(args: Array){

    val hashMap:HashMap = HashMap()
    hashMap.put(1,"Ajay")
    hashMap.put(3,"Vijay")
    hashMap.put(4,"Prakash")
    hashMap.put(2,"Rohan")

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

    hashMap.replace(3,"Ashu")
    hashMap.put(2,"Raj")
    println(".....hashMap.replace(3,\"Ashu\")... hashMap.replace(2,\"Raj\").......")....")
    for(key in hashMap.keys){
        println("Element at key $key = ${hashMap[key]}")
    }
}

输出：

.....traversing hashmap.......
Element at key 1 = Ajay
Element at key 2 = Rohan
Element at key 3 = Vijay
Element at key 4 = Prakash
.....hashMap.replace(3,"Ashu")...hashMap.put(2,"Raj")....
Element at key 1 = Ajay
Element at key 2 = Raj
Element at key 3 = Ashu
Element at key 4 = Prakash

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

如果HashMap中存在指定的键，则函数containsKey()返回true；如果不存在这样的键，则返回false。

函数containsValue()用于检查HashMap中是否存在指定的值。如果HashMap中存在value，它将返回true，否则返回false。

fun main(args: Array){

    val hashMap:HashMap = HashMap()
    hashMap.put(1,"Ajay")
    hashMap.put(3,"Vijay")
    hashMap.put(4,"Prakash")
    hashMap.put(2,"Rohan")

    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(\"Rohan\").......")
    println(hashMap.containsValue("Rohan"))
}

输出：

.....traversing hashmap.......
Element at key 1 = Ajay
Element at key 2 = Rohan
Element at key 3 = Vijay
Element at key 4 = Prakash
.....hashMap.containsKey(3).......
true
.....hashMap.containsValue("Rohan").......
true

Kotlin HashMap示例5-clear()

clear()函数用于清除HashMap中的所有数据。

fun main(args: Array){

    val hashMap:HashMap = HashMap()
    hashMap.put(1,"Ajay")
    hashMap.put(3,"Vijay")
    hashMap.put(4,"Prakash")
    hashMap.put(2,"Rohan")

    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)
}

输出：

.....traversing hashmap.......
Element at key 1 = Ajay
Element at key 2 = Rohan
Element at key 3 = Vijay
Element at key 4 = Prakash
.....hashMap.clear().......
.....print hashMap after clear().......
{}