Kotlin 中的 Getter 和 Setter [英] Getters and Setters in Kotlin

问题描述

例如，在 Java 中，我可以自己编写 getter(由 IDE 生成)或在 lombok 中使用诸如 @Getter 之类的注解——这非常简单.

In Java, for example, I can write getters on my own (generated by IDE) or use Annotations like @Getter in lombok - which was pretty simple.

Kotlin 具有默认情况下的getter 和setter.但我不明白如何使用它们.

Kotlin however has getters and setters by default. But I can't understand how to use them.

我想实现，比如说 - 类似于 Java:

I want to make it, lets say - similar to Java:

private val isEmpty: String
        get() = this.toString() //making this thing public rises an error: Getter visibility must be the same as property visibility.

那么getter是如何工作的呢?

So how do getters work?

推荐答案

Getter 和 setter 在 Kotlin 中自动生成.如果你写:

Getters and setters are auto-generated in Kotlin. If you write:

val isEmpty: Boolean

相当于下面的Java代码:

It is equal to the following Java code:

private final Boolean isEmpty;

public Boolean isEmpty() {
    return isEmpty;
}

在您的情况下，私有访问修饰符是多余的 - isEmpty 默认是私有的，只能由 getter 访问.当您尝试获取对象的 isEmpty 属性时，您实际上会调用 get 方法.为了更深入地了解 Kotlin 中的 getter/setter:下面的两个代码示例是相等的:

In your case the private access modifier is redundant - isEmpty is private by default and can be accessed only by a getter. When you try to get your object's isEmpty property you call the get method in real. For more understanding of getters/setters in Kotlin: the two code samples below are equal:

var someProperty: String = "defaultValue"

和

var someProperty: String = "defaultValue"
    get() = field
    set(value) { field = value }

我还想指出，getter 中的 this 不是您的财产 - 它是类实例.如果你想在 getter 或 setter 中访问字段的值，你可以使用保留字 field :

Also I want to point out that this in a getter is not your property - it's the class instance. If you want to get access to the field's value in a getter or setter you can use the reserved word field for it:

val isEmpty: Boolean
  get() = field

如果您只想在公共访问中使用 get 方法 - 您可以编写以下代码:

If you only want to have a get method in public access - you can write this code:

var isEmpty: Boolean
    private set 

由于靠近 set 访问器的 private 修饰符，您只能在对象内部的方法中设置此值.

due to the private modifier near the set accessor you can set this value only in methods inside your object.

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