Throwing exceptions

The following is a code snippet that demonstrates how exceptions can be thrown. You can paste it in the Scala console or in a Scala worksheet:

case class Person(name: String, age: Int)
case class AgeNegativeException(message: String) extends Exception(message)

def createPerson(description: String): Person = {
  val split = description.split(" ")
  val age = split(1).toInt
  if (age < 0)
    throw AgeNegativeException(s"age: $age should be > 0")
  else
    Person(split(0), age)

The createPerson function creates the Person object if the string passed in an argument is correct, but throws different types of exceptions if it is not. In the preceding code, we also implemented our own AgeNegativeException isntance, which is thrown if the age passed in the string is negative, as shown in the following code:

scala> createPerson("John 25")
res0: Person = Person(John,25)

scala> createPerson("John25")
java.lang.ArrayIndexOutOfBoundsException: 1
  at .createPerson(<console>:17)
  ... 24 elided

scala> createPerson("John -25")
AgeNegativeException: age: -25 should be > 0
  at .createPerson(<console>:19)
  ... 24 elided

scala> createPerson("John 25.3")
java.lang.NumberFormatException: For input string: "25.3"
  at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
  at java.lang.Integer.parseInt(Integer.java:580)
  at java.lang.Integer.parseInt(Integer.java:615)
  at scala.collection.immutable.StringLike.toInt(StringLike.scala:301)
  at scala.collection.immutable.StringLike.toInt$(StringLike.scala:301)
  at scala.collection.immutable.StringOps.toInt(StringOps.scala:29)
  at .createPerson(<console>:17)
  ... 24 elided

Since the exceptions are not caught by any try...catch block, the Scala console shows a stack trace. The stack trace shows all the nested function calls that led to the point where the exception was thrown. In the last example, the val age = split(1).toInt line in createPerson called scala.collection.immutable.StringOps.toInt, which called scala.collection.immutable.StringLike.toInt$, and so on, until finally the java.lang.Integer.parseInt function threw the exception at line 580 in Integer.java.