scala構築方法(デフォルトコンストラクタ)

        （  ）      



class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationClient {
...
def this() = this(new SparkConf())
}


java     ：
class Person(name String,age Int){
this.name=name;
this.age=age;
}

scala> ///////////////////

scala> class Person(newName : String){    --        
     |   var name = "Flink"
     |   var age = 10
     |   this.name = newName
     |   def this() = this(name)                --  0   
     |   def this(name : String,age : Int){     --  2   
     |   this(name)
     |   this.age = age
     |   }
     | }
defined class Person

scala> val p1 = new Person
p1: Person = Person@5a4b4bf3

scala> val p2 = new Person("Spark")
p2: Person = Person@47aa6f0b

scala> val p3 = new Person("Scala",3)
p3: Person = Person@5101d32a

scala> p1.name
res117: String = Flink

scala> p2.name
res118: String = Spark

scala> p3.name + p3.age
res119: String = Scala3

-------------------------------------------------------


scala> class Person(newName : String){
     |   var name = "Flink"
     |   var age = 10
     |   this.name = newName
     | }
defined class Person

scala> val p1 = new Person         --    
:17: error: not enough arguments for constructor Person: (newName: String)Person.
Unspecified value parameter newName.
       val p1 = new Person
                ^

scala> val p2 = new Person("Spark")
p2: Person = Person@41124730

scala> val p3 = new Person("Scala",3)     --    
:17: error: too many arguments for constructor Person: (newName: String)Person
       val p3 = new Person("Scala",3)
                ^

------------------------------------------------

scala> class Person(newName : String){
     |   var name = "Flink"
     |   var age = 10
     |   this.name = newName
     |   println("hello...")
     | }
defined class Person

scala> val p2 = new Person("Spark")
hello...            --         ，      
p2: Person = Person@336d1321

scala> p2.name
res130: String = Spark