Held: Tuesday, 17 September 2013

Back to Outline 10 - Exceptional Programming. On to Outline 12 - Interfaces and Polymorphism.

Summary

We continue our exploration of object-oriented programming by examining Java's approach to objects, the building blocks of oop.

Related Pages

• Reading: Classes
• Reading: Standard Object Methods
• Lab: Classes (won't be used)
• Homework: Fractions
• EBoard (Source) (PDF)

Overview

• A brief introduction to objects.
• A few tricks.
• Standard object methods.
• An exercise: Fractions.
• An exercise: Counters.

Administrivia

• Note: I seem to be pushing you harder than I'd like on the assignments. We'll do a demo of how not to approach these assignments.
• Note: I feel like a Grinnell student. I seem to have more work than I can physically do.
  • HW4 is in quick draft form.
  • I also expect to have the reading available late today.
• Reading for Wednesday: Interfaces
• EC Opportunities
  • Convocation noon, 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?

A Brief Introduction to Objects

• The core of object-oriented programming.
• Key idea one: Encapsulation.
  • Group methods and data.
  • Protect data (and some methods).
• In Java, we use template classes to build objects.
• The template specifies
  • The data (fields).
  • The methods.
  • The constructors.
• Fields look like variable declarations.
• Methods look like methods.
• Constructors look like methods with the same name as the class.

Side Notes

• You can cast objects.
  
  • You'll get a ClassCastException if Java can't convert them.
• The instanceof operation lets you determine whether an object can be cast.

Standard Object Methods

• Java classes are expected to have a few standard methods.
  • toString() - convert to a string
  • equals() - determine if this object equals another object
  • hashCode() - convert to a relatively unique integer
• There are also a few common methods
  • clone() - make a copy
  • compareTo() - compare to another object of the same type

Exercise: Fractions

• Let's continue our fraction exercise from HW2.

Another Exercise: Counters

• We'll also try to build counter objects.