Overview

• Preliminaries
  • Admin.
  • Questions on HW3
• Dealing with errors.
• Java's Exceptions.
• Lab.

Admin

• New partners for this week's labs.
• Dutch letters! Take half of one (if you'd like).
• Study break today at 8pm.
• Picnic Friday!
• VNC Instructions at http://www.cs.grinnell.edu/vnc
• 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
  • Standard Object Methods
• EC Opportunities
  • Convocation this Wednesday at noon. (Sam rants about the importance of convo. See the outline for details.)
  • 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)
  • Participate in Humans vs. Zombies. And yes, you can still get in.
  • Other?

Questions on HW3

• What should we return for part (the maknig change question): Choose one of these:
  • An array of numbers that give the count of each coin. 2, 7, 11, 54
    • For 28: 0, 4, 0, 0
    • Or 0, 28, 0, 0
  • An array of numbers that give the list of coin values.
  • DOCUMENT!
• Should we cite that Java API? It depends on how you use it. If you just look something up, I wouldn't bother. If you copy code, I would cite it.

Dealing with errors

• Some errors are the programmer's fault. We call those bugs.
• Some errors are beyond the programmer's control
  • Bad inputs
  • Missing files
• We need to think about errors
• Sam's model: Your code gets used by other code, gets used by the GUI, interacts with user
  • YOUR UTILITY CODE SHOULD NOT USE PRINTF TO REPORT ERRORS!
• In Java, we have Exceptions/Errors to report errors
  • Caller provides two places to return: Success/Failure

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A procedure that can fail

public static type proc(inputs) throws Exception

Fail

throw new Exception("reason");

Dealing with errors - throw your own

public static type caller(inputs) throws Exception { proc(...); }

Dealing with errors - Provide the alternate flow of control

public static type caller(inputs) { try { proc(...); ...; } catch (Exception e) { // RECOVER }

Lab

• Question 1: Autoflush makes it print output as soon as you print a newline. (or at least use println).
  • If you don't flush or close at the end, your last output gets dropped.