Custom Exception in scala

Question

how can i create custom exceptions in Scala extending Exception class and throw them when exception occurs as well as catch them.

example in java :

Answer 1

class MyException(message: String) extends Exception(message) {

  def this(message: String, cause: Throwable) {
    this(message)
    initCause(cause)
  }

  def this(cause: Throwable) {
    this(Option(cause).map(_.toString).orNull, cause)
  }

  def this() {
    this(null: String)
  }
}

This is almost identical to @Jacek L.'s answer. I just wanted to add some more input on the motive behind this answer.

Why so many constructors?

Throwable is written in kind of a funny way. It has 4 constructors -- ignoring the one with the boolean toggles -- each of them behaves a bit differently with nulls, and these differences could only be maintained with multiple constructors.

It would have been a bit cleaner if Scala would have allowed to call a superclass constructor via super, but it doesn't :(

Why not a case class?

• Perfectly maintaining the constructors' behavior regarding nulls wouldn't be possible; specifically, both def this() and def this(message: String) will have to set the cause to null, while originally it is set to this.
• toString will not be overridden.
• The message and the cause are already publicly available via getMessage and getCause. Adding another reference to these is redundant.
• equals will be overridden and will behave differently.
  Meaning, new Exception("m") == new Exception("m") // false
  while new CaseException("m") == new CaseException("m") // true

If one desires to access the message and the cause via pattern-matching, one can simply implement the unapply method:

object MyException {
  def unapply(e: MyException): Option[(String,Throwable)] = Some((e.getMessage, e.getCause))
}