Scala language learning-07-constructor

One 、 grammar

class  Class name (){
    

    // primary constructor 
    
    def this( Parameters : type ) = {
    
    
        // there this Is the key word , Represents an auxiliary constructor 
        // The number of parameters is defined by itself 
    }
    
    def this( Parameters : type , Parameters : type ) = {
    
    }

}

Two 、 matters needing attention

（1）this Is the key word , Represents an auxiliary constructor .

（2） Auxiliary constructors can have multiple .

（3）Scala The auxiliary constructor is distinguished by the difference of the incoming parameters .

（4） The secondary constructor must call the primary constructor .

（5） Formal parameters are not constructor attributes , Can't change .

3、 ... and 、 Test code

object TestClassInitMethod {
    
    def main(args: Array[String]): Unit = {
    
        var NewStudent: Student = new Student()
        var NewStudent_1: Student = new Student("Lxg")
        NewStudent.name = "Zxj"
        NewStudent.PrintInfo()
    
        var NewStudent1: Student1 = new Student1("Sun", 27)
        var NewStudent1_1: Student1 = new Student1("Lxg")
        NewStudent1.name = "Zxj"
        NewStudent1.PrintInfo()
    
        var NewStudent2: Student2 = new Student2("Moon", 30)
        var NewStudent2_1: Student2 = new Student2("Book")
        //NewStudent2.name = "Zxj" // Formal parameters are not constructor attributes , Can't change 
        NewStudent2.PrintInfo()
    }
}

// Nonparametric construction method 
class Student(){
    
    var name: String = "Czg"
    var age: Int = 18
    println("")
    println("========================")
    println(" The main constructor call of the parameterless constructor ！！！")
    println(s"name : ${
      name} , age : ${
      age}")
    
    def this(name: String) = {
    
        this()
        this.name = name
        println(" An auxiliary constructor call to a parameterless constructor ！！！")
        println(s"name : ${
      name} , age : ${
      age}")
    }
    
    def PrintInfo(): Unit = {
    
        println("++++++++++++++++++++++++")
        println(s"name : ${
      name} , age : ${
      age}")
    }
}

// Parametric construction method 
class Student1( var name: String, var age: Int){
    
    println("")
    println("========================")
    println(" The main constructor of the parameterized constructor calls ！！！")
    println(s"name : ${
      name} , age : ${
      age}")
    
    def this(name: String) = {
    
        this(name, 20)
        this.name = name
        println(" The auxiliary constructor of the parameterized constructor calls ！！！")
        println(s"name : ${
      name} , age : ${
      age}")
    }
    
    def PrintInfo(): Unit = {
    
        println("++++++++++++++++++++++++")
        println(s"name : ${
      name} , age : ${
      age}")
    }
}

// Formal parameter construction method 
class Student2(name: String, age: Int){
    
    println("")
    println("========================")
    println(" Main constructor call with formal parameter constructor ！！！")
    println(s"name : ${
      name} , age : ${
      age}")
    
    def this(name: String) = {
    
        this(name, 20)
        //this.name = name
        println(" Auxiliary constructor call with formal parameter constructor ！！！")
        println(s"name : ${
      name} , age : ${
      age}")
    }
    
    def PrintInfo(): Unit = {
    
        println("++++++++++++++++++++++++")
        println(s"name : ${
      name} , age : ${
      age}")
    }
}

Four 、 test result

========================
 The main constructor call of the parameterless constructor ！！！
name : Czg , age : 18

========================
 The main constructor call of the parameterless constructor ！！！
name : Czg , age : 18
 An auxiliary constructor call to a parameterless constructor ！！！
name : Lxg , age : 18
++++++++++++++++++++++++
name : Zxj , age : 18

========================
 The main constructor of the parameterized constructor calls ！！！
name : Sun , age : 27

========================
 The main constructor of the parameterized constructor calls ！！！
name : Lxg , age : 20
 The auxiliary constructor of the parameterized constructor calls ！！！
name : Lxg , age : 20
++++++++++++++++++++++++
name : Zxj , age : 27

========================
 Main constructor call with formal parameter constructor ！！！
name : Moon , age : 30

========================
 Main constructor call with formal parameter constructor ！！！
name : Book , age : 20
 Auxiliary constructor call with formal parameter constructor ！！！
name : Book , age : 20
++++++++++++++++++++++++
name : Moon , age : 30

 Process ended , Exit code 0