Exception handling

In Scala exceptions are not checked so effectively all exceptions are runtime exceptions. When you want to handle exceptions you use a try {...} catch {...} block like you would in Java except that the catch block uses matching to identify and handle the exceptions. This creates a very powerful but light-weight way to handle exceptions:

1. scala> def handle( f: => Unit ) = {
2.      | try { f } catch {
3.      | case _:AssertionError => println ("Whoops an assertion error")
4.      | case r:RuntimeException => println ("Runtime Exception: "+ r.getStackTraceString)
5.      | case e if (e.getMessage == null) => println ("Unknown exception with no message")
6.      | case e => println ("An unknown error has been caught" + e.getMessage)
7.      | }
8.      | }
9. handle: (=> Unit)Unit
11. scala> handle { throw new AssertionError("big bad error") }
12. Whoops an assertion error
14. scala> handle { throw new IllegalArgumentException("Sooooo illegal") }
15. Runtime Exception: line9$object$$iw$$iw$$iw$$anonfun$1.apply(:8)
16. line9$object$$iw$$iw$$iw$$anonfun$1.apply(:8)
17. line7$object$$iw$$iw$$iw$.handle(:7)
18. line9$object$$iw$$iw$$iw$.(:8)
19. line9$object$$iw$$iw$$iw$.()
20. RequestResult$line9$object$.(:3)
21. RequestResult$line9$object$.()
22. RequestResult$line9$object.result()
23. sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
24. sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
25. sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
26. java.lang.reflect.Method.invoke(Method.java:597)
27. scala.tools.nsc.Interpreter$Request.loadAndRun(Interpreter.scala:889)
28. scala.tools.nsc.Interpreter.interpret(Interpreter.scala:508)
29. scala.tools.nsc.Interpreter.interpret(Interpreter.scala:494)
30. scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:242)
31. scala.tools.nsc.InterpreterLoop.command(InterpreterLoop.scala:230)
32. scala.tools.nsc.InterpreterLoop.repl(InterpreterLoop.scala:142)
33. scala.tools.nsc.InterpreterLoop.main(InterpreterLoop.scala:298)
34. scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:141)
35. scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
37. scala> handle{ throw new java.io.IOException("cant read something") }
38. An unknown error has been caughtcant read something