Constructor use null value as parameter

Question

Following is a simple scala class definition, there are 2 constructors defined inside Person class.

Person.scala:

// class that has field and method,
class Person(var name:String, var age:Short) {
    def this() {
        this("", 0);
    }
    def this(name:String) {
        this(name, 0);
    }
    def hi() = printf("hi, I am %s!\n", name)
}

// var nobody = new Person();
var eric = new Person("Eric", 12);
eric.hi;

The question is:

When age field is not provided in constructor's argument list, I want to initialize it to null, not 0, what is the proper way to do that. Same requirement for the name field.

Dont use null then, use Option: case class Person(name: Option[String]=None, age:Option[Int] = None) and then you dont need all those boiler plate constructors — maress
– maress, Commented Aug 12, 2016 at 12:36
Firstly, as @maress said, it's not scala way to use null. Secondly, you can't assign null to Short (AnyVal) value. — Sergii Lagutin
– Sergii Lagutin, Commented Aug 12, 2016 at 12:38

John K · Accepted Answer · 2016-08-12 12:44:16Z

1

So basically the scala class you wanted to create is

case class Person(name:String, age:Option[Short] = None) {
    def hi() = println(s"hi, I am $name.\nMy age is ${age.getOrElse("not provided")}.")
}

Which returns

scala> var eric = new Person("Eric", Some(12));
eric: Person = Person(Eric,Some(12))

scala> eric.hi
hi, I am Eric.
My age is 12.

scala> var eric = new Person("Eric");
eric: Person = Person(Eric,None)

scala> eric.hi
hi, I am Eric.
My age is not provided.

answered Aug 12, 2016 at 12:44

John K

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2 Comments

Eric Over a year ago

I have one doubt, this(name, None); in this expression, what is the None means? Is it a value defined somewhere, or it created an object of type None?

John K Over a year ago

Here is a link from the documentation explaining what Options are.

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