CSC152 2005F, Class 26: Review of Exceptions

Admin
* Continuing strategy of last week
* Data collection: Second year retreat

Overview
* Parsing, continued

Parsing, Continued
* Two concerns!
  * What happens when someone writes a number too large?
  * What happens when we hit a non-digit?
* As a programmer, you need to decide what to do when you encounter one of these kinds of errors.
  * Preparation: Think about when these errors might occur.
  * Reaction:
    * "Pass the buck"; Throw an exception
    * "Pass the buck"; Return a special value
    * Skip the erroneous stuff (ignore non-digits; stop before overflow)
    * Stop as soon as you hit an error and assume that the erroneous stuff belongs to another part of the program
    * Print an error message (NO!)
    * Return a different kind of value (or restart the process in a different way). (HARD)
    * Set a precondition and let the caller suffer if the precondition is not met.
* As a Java programmer, throwing exceptions is likely to be your default behavior.
  * Permits the *caller* to decide what is best to do.

        try {
          int digit = charToInt(str.charAt(pos));
          result = result + digit * place;
          place = place*10;
        }
        catch (Exception e)
        {
          // Skip offending character.
        }