Kotlin中的吸气剂和吸气剂 [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)，也可以在lombok中使用@Getter之类的注解-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.

但是，科特林默认具有 getter和setter . 但是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.

我想说-与Java类似:

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.

那么吸气剂如何工作?

So how do getters work?

推荐答案

字母和设置者是在Kotlin中自动生成的.如果您写:

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

val isEmpty: Boolean

它等于以下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-默认为isEmpty是私有的，并且只能由getter访问.当您尝试获取对象的isEmpty属性时，将实际调用get方法.为了进一步了解Kotlin中的getter/setter方法，以下两个代码示例相等:

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 }

另外，我想指出的是，getter中的this不是您的属性-它是类实例.如果要在getter或setter中访问字段的值，则可以为其使用保留字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set访问器附近的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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