CSC207.01 2014S, Class 13: Some Subtleties: References and Automatic Boxing/Unboxing

Overview

Preliminaries

While you're waiting for real class to start, fork and clone the repo for the lab https://github.com/Grinnell-CSC207/lab-boxing.
Reminder: Lab writeups get sent to me, and not the grader.
You should have received grades on HW2 along with an anonymous detailed grade sheet.
Now that I've graded writeup 8, we should talk for a few minutes about Exceptions.
Does anyone else need a partner for HW4?
When I write "Fine", what does it mean to you?
Mentor session tonight at 7pm in 3821. A good chance to ask questions (retrospectively on topics and prospectively on homework). And the study break is immediately thereafter.
Extra credit:
- CS Extra Thursday at 4:30: Stone on Red/Black Trees
- CS Table Friday at noon: Law, Order, and Computers
- More?

Readings for Tuesday: Interfaces, Polymorphism, Weiss 4
- Weiss 4 lasts the whole week, you need not do the whole thing.
No writeup today!
Continue to work on HW4. (Or start HW4, for the slackers.)

How do I test for an exception?

try
  {
    CodeThatShouldThrowAnException();
    fail("Exception was not thrown"); 
  }
catch (Exception e)
  {
    // Success!
  }

Do we have to support PEMDAS (aka order-of-operations)?

No. I would not expect you to figure out the algorithm on your own.

If we find a way to support PEMDAS (say, on StackOverflow), will we get extra credit?

Maybe.

What operations should we support?

Addition, Subtraction, Multiplication, Division, Negation, Store in register

Can you explain the register/storage elements?

Kind of like the store/recall button, but textual

r0 = 2 * 3
r1 = r0 * r0

Do we have to support multiple assignments on one line, as in the following?

r0 = r1 = r2 = 2

No.

Do we have to worry about the calculator equals, which means print?

No. The = is just assignment. Print the value after each line

If you had to write a hash code for fractions, what would you do?

return this.num.hashCode * prime1 + this.denom.hashCode * prime2;

Why won't the following work?

obj = new Integer((obj.intValue())++);

It's similar to writing 5++. You increment variables, not values.

Some lessons from the Exceptions lab.

You can return different exceptions for different situations.
- The client can choose appropriate responses for each situation.
You can design your own exceptions (and it doesn't take much work).
catch clauses are tried in order.
You should probably throw exceptions on bad input (or recover from bad input) rather than returning a special value.