Overview

• Preliminaries.
  • Admin.
  • Questions.
• Quick recap.
• Lab.

Preliminaries

Admin

• When physicists do math ...
• Reminder: Homework assignments get sent to the graders grader-207@cs.grinnell.edu, not to me.
• At yesterday's review session, I went over possible solutions to the CSV and calculator problems.
  • Lacking other questions, I will use review sessions to write homework solutions "live", as it were.
• I'll reserve a few minutes for questions on the homework.
• Extra credit:
  • CS Table Today: NP Completeness
  • CS Extra next Week: Stone on Red/Black Trees
  • More?

Upcoming Work

• Readings for Monday: References and Autoboxing/Autounboxing.
  • Not yet written.
  • Probably available Saturday.
• Today's writeup, Exercise 11
  • Subject: CSC 207 Writeup 8: Exceptions (YOUR NAME)
  • Due Monday.
• Work on Homework 4!

Questions

A Quick Recap

• Utility procedures fail

  • Old model: Crash the program

  • C model: Return special value

    foo = malloc (100 * sizeof(mystruct)); if (foo == null) ...

  • Java model: Two return mechanisms, normal and exceptional
    • Client of utility procedure MUST deal with the exception
• Your world when programming
  • You write utility code, so you must report to your caller throws Exception - can fail throw new Exception(...) - fail
  • You call other procedures, you must deal with potential exceptions try { code that may fail } catch (Exception e) { ... } throws Exceptions

• You can use different kinds of exceptions to signal kinds of errors

  public class DivergentSeriesException extends Exception { public DivergentSeriesException () { super(); } //

  public DivergentSeriesException (String str) { super(str); } // }

• Once we write that garbage, we can say `throw new DivergentSeriesException("Earnest says 'No!'");

  try { doStringTheory(); } catch (DivergentSeriesException dse) { System.out.println("Physicists don't believe series diverge."); } catch (Exception e) { System.out.println("Please switch universes."); }

Lab

How do I test the quadratic root?

Make some quadratics whose roots you know. For example (x-3)(x+2) = x^2-x-6. The smaller root is -2.

What does assertEquals look like for doubles?

public static void assertEquals(java.lang.String message,
                                double expected,
                                double actual,
                                double delta)

How do I make an inputstreamreader?

BufferedReader eyes =
    new BufferedReader(new InputStreamReader(System.in));

How do I convert a string to a double?

double d = Double.parseDouble(str);

Recent technical interview question

• You have a list of 1000 elements, containing all but one of the values 0 ... 1000 How do you find the missing value?