如何在科特林使用地图 [英] How to work with Maps in Kotlin

问题描述

下面的代码创建一个名为nameTable的新映射，然后向其中添加一个名为example的条目，然后尝试打印Value的name属性.

The code below is creating a new map called nameTable, then adding an entry named example to it, then trying to print the name property of the Value.

当我运行它时，加号操作似乎并没有像我想的那样向地图添加新条目.

When I run it, it seems that the plus operation didn't add a new entry to the map like I thought it would.

那么我在做什么错了?

So what am I doing wrong?

class Person(name1: String, lastName1: String, age1: Int){
    var name: String = name1
    var lastName: String = lastName1
    var age: Int = age1
}

var nameTable: MutableMap<String, Person> = mutableMapOf()
var example = Person("Josh", "Cohen", 24)

fun main (args: Array<String>){
    nameTable.plus(Pair("person1", example))
    for(entry in nameTable){
        println(entry.value.age)
    }
}

我们在这里，我会喜欢一些如何在地图上添加，删除和获取条目的示例.

While we're at it, I would love some examples of how to add, remove, and get an entry from a map.

推荐答案

您感到困惑的原因是plus不是 变异运算符，意味着它适用于(只读) Map，但不会更改实例本身.这是签名:

The reason for your confusion is that plus is not a mutating operator, meaning that it works on (read-only) Map, but does not change the instance itself. This is the signature:

operator fun <K, V> Map<out K, V>.plus(pair: Pair<K, V>): Map<K, V>

您想要的是在MutableMap上定义的变异运算符set:

What you want is a mutating operator set, defined on MutableMap:

operator fun <K, V> MutableMap<K, V>.set(key: K, value: V)

因此，您的代码可能会被重写(具有一些其他增强功能):

So your code may be rewritten (with some additional enhancements):

class Person(var name: String, var lastName: String, var age: Int)

val nameTable = mutableMapOf<String, Person>()
val example = Person("Josh", "Cohen", 24)

fun main (args: Array<String>) {
    nameTable["person1"] = example

    for((key, value) in nameTable){
        println(value.age)
    }
}

这篇关于如何在科特林使用地图的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！