kotlin 构造函数

主要建设者 (Primary Constructor)

• A Kotlin class have Primary constructor and one or more Secondary constructor.

  Kotlin类具有Primary构造函数和一个或多个Secondary构造函数。

• In Kotlin, Primary Constructor is the Part of Class Header.

  在Kotlin中，主要构造函数是类标题的一部分。

• Syntax:

  句法：

  class <Class Name> constructor(<optional Parameters>){
  // Class Body
  }
  
  

• The default visibility of the constructor will be public.

  构造函数的默认可见性将是public。

• Parameter of the primary constructor can be used in property initializer, declared in the class body.

  可以在类体内声明的属性初始化程序中使用主构造函数的参数。

演示Kotlin中主要构造函数示例的程序 (Program to demonstrate the example of Primary Constructor in Kotlin)

// Declare Class, with Primary Constructor keyword, 
// with one Parameter
class Dog constructor(name:String){
// Used Constructor Parameter to initialize property
// in class body
// String? for nullable property, 
// so property also contain null
private var name:String?=name
fun getDogName(): String?{
return name
}
}
/*
A) Constructor Keyword can be omitted if constructor 
does not have annotations and visibility modifiers.
*/
// Declare class, omitted Constructor Keyword
class Horse (name:String){
// Used Constructor Parameter to 
// initialize property in class body
private var name:String =name.toUpperCase()
fun getHorseName(): String?{
return name
}
}
/*
A) Kotlin has concise Syntax to declaring property 
and initialize them from primary constructor.
class Employee(var empName:String, val salary:Int)
B) same way as regular properties declaration, 
properties declare in primary constructor can be 
var (mutable) or val (immutable)
*/
// Declare class, Properties declare  in primary constructor
class Cat(private var name:String, private val age:Int){
fun setCatName(name:String){
this.name =name
}
fun printData(){
println("Name : $name and Age : $age")
}
}
// Main Function, entry Point of Program
fun main(args:Array<String>){
// Create Dog Class Object
val dog = Dog("tommy")
println("Dog Name : ${dog.getDogName()}")
// Create Horse Class object
val horse =Horse("Chetak")
println("Horse Name : ${horse.getHorseName()}")
// Create Cat Class object
val cat = Cat("Katrina",32)
cat.printData()
cat.setCatName("Micy")
cat.printData()
}

Output:

输出：

Dog Name : tommy
Horse Name : CHETAK
Name : Katrina and Age : 32
Name : Micy and Age : 32

翻译自: https://www.includehelp.com/kotlin/example-of-primary-constructor.aspx

kotlin 构造函数