Kotlin Reference (八) 可见性修饰符， data class，object Claz

KotLin 相关文档

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官方在线Reference
kotlin-docs.pdf
Kotlin for android Developers 中文翻译
Kotlin开发工具集成，相关平台支持指南
Kotlin开源项目与Libraries
Kotlin开源项目、资源、书籍及课程搜索平台
Google’s sample projects written in Kotlin
Kotlin and Android

 

可见性修饰符(visibility modifiers)

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Classes, objects, interfaces, constructors, functions, properties and their setters can have visibility modifiers.
Getters always have the same visibility as the property.
There are four visibility modifiers in Kotlin: private , protected , internal and public .
The default visibility, used if there is no explicit modifier, is public .

fun baz() {} //default public, it will be visible everywhereprivate class Bar {}  //private , it will only be visible inside the file containing the declarationinternal fun Bas() {} //internal , it is visible everywhere in the same module(an IntelliJ IDEA module; a Maven or Gradle project; a set of files compiled with one invocation of the Ant task)//protected class Bz  //protected is not available for top-level declarations.class Human {//or interface//    — private     // this class only visible//    — protected   // same as private + visible in subclasses too//    — internal    // 在module中 任何能访问该类的client//    — public      // 任何能访问该类的client}class C private constructor(a: Int) {} //the primary constructor visible this class onlyinternal class D /*internal or public*/ constructor(a: Int) {} //constructor: visible internalfun local() {//    public val c = 10    /*    Local variables, 不具有可见性修饰语     */}

 

使用data class声明class

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data class 特性：

1. 所有声明在主构造函数中的属性都会派生出相应的get/set(set需要属性为var)
   还会自动生成：

   equals() ，hashCode()
   toString() of the form “User(name=John, age=42)” ,
   copy() ，比如下面的 Human类的默认实现就是：fun copy(id: Int = this.id) = Human(id)

   如果类中实现或重写了某个函数后，那这个函数就不会再自动生成了()
    

2. data class 声明时，前面不能有 abstract, open, sealed or inner

3. 必须声明主构造函数，且至少有一个参数

data class 示例

open class Human(id: Int) {    override fun toString(): String {        return "Human"    }}data class User(val id: Int, val name: String, var age: Int): Human(id) {    var weight: Float = 0.0f    constructor(id: Int, weight: Float) : this(id, "", 18) {        this.weight = weight    }//    override fun toString(): String {//        return "User"//    }}

User继承了Human(id)，主构造函数有三个参数，内部还定义了一个有两个参数的构造函数。

初始化：

var u = User(1, "stone", 28) //id=1, name="stone", age=28u = User(2, 1.0f) //id=2, name="", age=18u.copy()u.copy(2)u.copy(2, "stone2")u.copy(2, "stone2", 27)

对于自动生成的copy方法，会根据主构造函数的参数上，来生成。
会对每个参数给定默认值(即原对象属性的值)，所以，调用时可以少传或不传参数

 

使用object声明class

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如下，使用object 声明一个ObjClass类：

object ObjClass {    const val const5 = 4    fun staticMethod() {}}

会成一个ObjClass的单例类，对于属性类似data class，会自动生成相应的getter、setter；成员的访问，类似java中的static形式；即[className].member