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 
        
          constructor(
         
          ){    // 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 Parameterclass 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 Keywordclass 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 constructorclass 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 Programfun main(args:Array
    
     ){    // 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 : tommyHorse Name : CHETAKName : Katrina and Age : 32Name : Micy and Age : 32

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kotlin 构造函数