Kotlin-了解Getter和Setters [英] Kotlin - Understanding Getters and Setters

问题描述

Kotlin会自动生成它的吸气剂和设置，但我从未提及它们吗?另外，用Kotlin编写自定义getter/setter的正确方法是什么?当我说myObj.myVar = 99时，我觉得myVar是我直接访问的myObj的公共字段吗?这里到底发生了什么?

Kotlin auto-generates it's getters and settings, but I never refer to them? Also, what is the correct way to write a custom getter/setter in Kotlin? When I say myObj.myVar = 99 I feel like myVar is a public field of myObj that I'm accessing directly? What is actually happening here?

推荐答案

在一些地方已经回答了这个问题，但是我想我会为从Java/C#/C/C ++过渡到Kotlin的人们分享一个具体的例子，以及谁有与我相同的问题:

This has been answered in a few places, but I thought that I would share a concrete example for people transitioning to Kotlin from Java/C#/C/C++, and who had the same question that I did:

我在理解gett和setter在Kotlin中的工作方式时遇到了困难，尤其是因为它们从未被显式调用(就像在Java中一样).因此，我感到不舒服，因为好像我们只是直接将vars/vals称为字段一样.因此，我进行了一个小实验来证明事实并非如此，实际上，当您访问变量/值时，实际上是在Kotlin中调用的是隐式(自动生成)或显式的getter/setter.区别在于，您没有明确要求默认的getter/setter.

I was having difficulty in understanding how getters and setters worked in Kotlin, especially as they were never explicitly called (as they are in Java). Because of this, I was feeling uncomfortable, as it looked like we were just directly referring to the vars/vals as fields. So I set out a little experiment to demonstrate that this is not the case, and that in fact it is the implicit (auto-generated) or explicit getter/setter that is called in Kotlin when you access a variable/value. The difference is, you don't explicitly ask for the default getter/setter.

文档中-声明属性的完整语法为:

From the documentation - the full syntax for declaring a property is:

var <propertyName>: <PropertyType> [= <property_initializer>]
   [<getter>]
   [<setter>]

我的例子是

class modifiersEg {

/** this will not compile unless:
 *      - we assign a default here
 *      - init it in the (or all, if multiple) constructor
 *      - insert the lateinit keyword    */
var someNum: Int?
var someStr0: String = "hello"
var someStr1: String = "hello"
    get() = field  // field is actually this.someStr1, and 'this' is your class/obj instance
    set(value) { field = value }

// kotlin actually creates the same setters and getters for someStr0
// as we explicitly created for someStr1

var someStr2: String? = "inital val"
    set(value) { field = "ignore you" }

var someStr3: String = "inital val"
    get() = "you'll never know what this var actually contains"

init {
    someNum = 0

    println(someStr2) // should print "inital val"

    someStr2 = "blah blah blah"
    println(someStr2) // should print "ignore you"

    println(someStr3) // should print "you'll never know what this var actually contains"
}

我希望对其他一些人有帮助吗?

I hope that helps to bring it all together for some others?

这篇关于Kotlin-了解Getter和Setters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！