private[this] vs private

Question

In Scala I see such feature as object-private variable. From my not very rich Java background I learnt to close everything (make it private) and open (provide accessors) if

Answer 1

Should I always use it by default? Or should I use it only in some specific cases where I need to explicitly restrict changing field value even for objects of the same class? In other words how should I choose between

It's better to use private[this] if you plan to synchronize the variable.

Here a good example from the scala style guide of the Spark team:

// The following is still unsafe.
class Foo {
  private var count: Int = 0
  def inc(): Unit = synchronized { count += 1 }
}

// The following is safe.
class Foo {
  private[this] var count: Int = 0
  def inc(): Unit = synchronized { count += 1 }
}