Handle java.lang.NullPointerException in Scala

Question

Say I have a model class as shown below:

class User () {
  var id: Option[java.lang.Long] = _
  var name: Option[String] = _
  var date: Option[java.util.Date] = _

  def this(id: java.lang.Long,name: String, date: java.util.Date){
    this()
    this.id=Option(id)
    this.name=Option(name)
    this.date=Option(date)
  }
}

I tried to create an object by doing

var obj = new User
obj.id=12345
obj.name=user

Obviously obj.date is null, and I kept getting a java.lang.NullPointerException at this point. How should I handle this exception?

Why do you need a zero-arg constructor? If you're going to initialise the fielsds immediately, have a constructor do that (then that can initialise the date field appropriately -i.e. None) — The Archetypal Paul
– The Archetypal Paul, Commented May 26, 2016 at 8:17
@JonnyHenly, it's not clear to me that lazy vals are needed or desirable here. — The Archetypal Paul
– The Archetypal Paul, Commented May 26, 2016 at 8:18
@TheArchetypalPaul I need to initialize because it just wont write to my neo4j if i dont. I am still grasping the enviroment. — kenlz
– kenlz, Commented May 26, 2016 at 8:19
So def this(id: java.lang.Long,name: String){this() this.id=Option(id) this.name=Option(name) this.date=None} — The Archetypal Paul
– The Archetypal Paul, Commented May 26, 2016 at 8:21

Yuval Itzchakov · Accepted Answer · 2016-05-26 08:33:47Z

3

I would advise you to initialize the values directly through the constructor. This looks like a POSO (Plain Old Scala Object), so maybe you would be better off with an immutable case class:

case class User(id: Option[Long], name: Option[String], date: Option[Date])

Now if you want to initialize only some of the properties, you can either pass None or create an auxiliary constructor via the companion object:

case class User(id: Option[Long], name: Option[String], date: Option[Date])
object User {
  def apply(id: Option[Long], name: Option[String]) = {
    User(id, name, None)
  }
}

Edit:

If Java interop is important, you can define multiple constructors inside the case class which will be visible in Java:

case class User(id: Option[Long], name: Option[String], date: Option[Date]) {
  def this(id: Long, name: String) = {
    this(Some(id), Some(name), None)
  }
}

edited May 26, 2016 at 8:33

answered May 26, 2016 at 8:20

Yuval Itzchakov

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4 Comments

kenlz Over a year ago

I tried that in the first attempt, but then it wont let me write to neo4j using spring-data-neo4j driver, but this way seems to do it.

Yuval Itzchakov Over a year ago

but then it wont let me write to neo4j using spring-data-neo4j driver What does that mean? What happens when you attempt to write something?

kenlz Over a year ago

successful with no error but the model wasnt inserted

Sergey Over a year ago

@kenlz Perhaps spring-data-neo4j requires your classes to be complying JavaBeans. To achieve that with scala case classes, either annotate every field with a @BeanProperty, or define your own getters in vanilla java format.

Rüdiger Klaehn · Accepted Answer · 2016-05-26 08:08:05Z

1

One nice thing about Option[T] is that it has a safe default value None. So initialise your vars to None instead of null.

You should also think about making your model class immutable.

answered May 26, 2016 at 8:08

Rüdiger Klaehn

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2 Comments

kenlz Over a year ago

I tried that, and I get a java.lang.ClassCastException: scala.None$ cannot be cast to java.util.Date, I think i need to manually initialize a default Date value if null were found

The Archetypal Paul Over a year ago

@kenlz, please update the question with your code because that doesn't sound correct. You assign None to an Option[Date], not a Date

Shivansh · Accepted Answer · 2016-05-26 08:29:59Z

0

More easy way to do this is

case class User(id: Option[Long]=None, name: Option[String]=None, date: Option[Date]=None)

In this case if you give a value it takes the value or else it would take None as a default value.

answered May 26, 2016 at 8:29

Shivansh

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