快学scala第五章习题之构造器

快学scala第五章习题之构造器：

6.8 创建一个Car类，以只读属性对应制造商，型号名称，型号年份以及一个可读写的属性用于车牌。提供四组构造器。每个构造器fc都要求制造商和型号为必填。型号年份和车牌可选，如果未填，则型号年份为-1，车牌为空串。你会选择哪一个作为你的主构造器？为什么？ 

选择四个属性的，其他构造器可以在此基础上直接赋值

代码：

package Chapter5

object Car5 {
   def main(arg:Array[String]){
    var car1=new Car("BWM","A6")
    car1.PrintAll()
     var car2=new Car("BWM","A6",2000)
    car2.PrintAll()
     var car3=new Car("BWM","A6","A01")
    car3.PrintAll()
     var car4=new Car("BWM","A6",2000,"A01")
    car4.PrintAll()
   }
   
  class Car( val producerName:String,val productName:String,val productyear:Int,var num:String){
    def this( producerName:String, productName:String){
      this(producerName, productName,-1,"")
      
    }
    def this( producerName:String, productName:String,productyear:Int){
      this(producerName, productName,productyear,"")
    }
    def this( producerName:String, productName:String,num:String){
      this( producerName:String, productName:String,-1,num)
    }
    def PrintAll(){
      println("producerName:"+producerName+" productName:"+productName+" productyear:"+productyear+" num:"+num)
    }
  }
}

执行结果：

producerName:BWM productName:A6 productyear:-1 num:
producerName:BWM productName:A6 productyear:2000 num:
producerName:BWM productName:A6 productyear:-1 num:A01
producerName:BWM productName:A6 productyear:2000 num:A01