Kotlin 的引导者和引导者

在 Kotlin，读取器和设置器都是自动生成的。如果你写道:

val isEmpty: Boolean

它等于以下 Java 代码:

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 在默认情况下是私有的，只能由 getter 访问。当您尝试获取对象的 isEmpty 属性时，您将在 real 中调用 get 方法。为了更好地理解 Kotlin 的 getters/setter，下面的两个代码示例是相等的:

var someProperty: String = "defaultValue"

and

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

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

如果你只想在公共访问中有一个 get 方法，你可以写下面的代码:

var isEmpty: Boolean
private set

由于 set 访问器附近的私有修饰符，因此只能在对象内部的方法中设置此值。

关于属性访问器 可见度修饰符可见度修饰符的规则如下:

• var和 val属性的 Getter 可见性应该与该属性的 一样完全相同，因此您只能显式地复制属性修饰符，但它是多余的:

  protected val x: Int
  protected get() = 0 // No need in `protected` here.
  

• Setter visibility of var property should be the same or less permissive than the property visibility:

  protected var x: Int
  get() = 0
  private set(x: Int) { } // Only `private` and `protected` are allowed.
  

In Kotlin, properties are always accessed through getter and setter, thus there's no need in making a property private with public accessors like in Java -- its backing field (if present) is already private. So, visibility modifiers on property accessors are only used to make setter visibility less permissive:

• For a property with backing field and default accessors:

  var x = 0 // `public` by default
  private set
  

• For a property without backing field:

  var x: Int // `public` by default
  get() = 0
  protected set(value: Int) { }
  

Kotlin 中的 Getter 在默认情况下是公共的，但是您可以将 setter 设置为 private，并通过在类中使用一个方法来设置值。像这样。

/**
* Created by leo on 17/06/17.*/


package foo
class Person() {
var name: String = "defaultValue"
private set


fun foo(bar: String) {
name = bar // name can be set here
}
}


fun main(args: Array<String>) {
var p = Person()
println("Name of the person is ${p.name}")
p.foo("Jhon Doe")
println("Name of the person is ${p.name}")
}

更多信息可以参见本教程:

Android 开发者的另一个 Kotlin 教程

物业

在 Kotlin 世界中，类不能有字段，只能有 properties. var keyword tells us the property is mutable, in contrast to val. Let’s 举个例子:

class Contact(var number: String) {


var firstName: String? = null
var lastName: String? = null
private val hasPrefix : Boolean
get() = number.startsWith("+")


}

虽然没有很多代码，但是在 我们将一步一步来。首先，我们创建了一个 公共期末班联系

This is the primary rule we have to face: if not specified otherwise, 默认情况下，类是公共的和最终的(顺便说一下，对于 如果要从类继承，请将其标记为 open keyword.

1) Kotlin propertyfirstName的默认 setter和 getter示例

class Person {
var firstName: String = ""
get() = field       // field here ~ `this.firstName` in Java or normally `_firstName` is C#
set(value) {
field = value
}


}

吸毒

val p = Person()
p.firstName = "A"  // access setter
println(p.firstName) // access getter (output:A)

如果你的 setter或 getter是 一模一样以上，你可以移除它，因为它是 不必要的

const val PREFIX = "[ABC]"


class Person {


// set: if value set to first name have length < 1 => throw error else add prefix "ABC" to the name
// get: if name is not empty -> trim for remove whitespace and add '.' else return default name
var lastName: String = ""
get() {
if (!field.isEmpty()) {
return field.trim() + "."
}
return field
}
set(value) {
if (value.length > 1) {
field = PREFIX + value
} else {
throw IllegalArgumentException("Last name too short")
}
}
}

val p = Person()
p.lastName = "DE         " // input with many white space
println(p.lastName)  // output:[ABC]DE.
p.lastName = "D" // IllegalArgumentException since name length < 1