Scala nest data structure

Question

I am new to scala programming language

In java if I have a data structure like HashMap<Integer,HashSet<LinkedList>>

If I don't initialize HashSet, I will get NullpointerException.

But in Scala, if I have HashMap<Int,HashSet<ListBuffer[Int]>>

How do I initialize nested HashSet?

When I use get() method.Should I use pattern match like

case Some =>

case None =>

Answer 1

Pattern matching as you describe is a good option.

An other one is to use getOrElse :

map.getOrElse(10, Set.empty)