Held: Monday, 16 September 2013

Back to Outline 09 - Input and Output. On to Outline 11 - Classes, Objects, and Interfaces.

Summary

We consider Java's standard mechanism for reporting and recovering from errors.

Related Pages

• Reading: Exceptions
• Lab: Exceptions
• EBoard (Source) (PDF)

Overview

• Dealing with errors.
• Java's Exceptions.
• Lab.

Administrivia

• The Math/CS picnic is this Friday. I'll pass around sign-up cards.
• Exception handling is one of the first places where my students start saying "Java is your nanny." Can you tell why?
• I managed to finish reviewing HW1 this weekend. You should have my responses. You can also see answers to most questions in the FAQ.
• I'll reserve time in class today for questions on HW3.
• I expect to have the next homework available tomorrow.
• Readings for Tuesday: Writing Your Own Classes and Standard Object Methods.
• EC Opportunities
  • Convocation this Wednesday.
  • Learning from Alumni Thursday @ 2:15 Sam Tape and company.
  • CS Extras Thursday @ 4:30: Kim Spasaro on Linguistics Programming
  • CS Table Friday (pair programming)
  • Other?

On the importance of Scholars Convocation. I went to a school that had a large common core. It was almost guaranteed that you or your roommate had read Freud, Plato, Kuhn, and Adam Smith. And that shared knowledge meant that discussions of any topic could draw upon those ideas. As much as I love the open curriculum (or whatever term they have for it this week), I regret that Grinnell students have no shared knowledge base (other than what you get from Tutorial, and Tutorials vary significantly). I think we'd have a higher level of academic discussion if everyone went to every convocation, and so encourage ever student to do so.

When things go wrong

• Things go wrong in programs. You get bad input. Files you expect to be there aren't there. Clients don't pay attention to preconditions.
• Two wrong approaches:
  • Crash the program
  • Report the error to the user
• A correct approach
  • Report the error to the caller
• In Java, we report errors to callers with exceptions

The basis of exceptions

• Indicate that a procedure may fail with throws Exception
• Indicate that a procedure fails with throw Exception

Lab