Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • About Exam 1.
  • Questions.
• Questions on Polymorphism.
• Questions on Inheritance.
• Labs.

Preliminaries

Admin

• It appears that snow is more of a deterrant than cold.
• I will not be holding a review session tomorrow. Sorry.
• Finish the polymorphism lab before beginning the inheritance lab.
• Extra credit:
  • CS Extra Thursday at 4:30: Stone on Red/Black Trees
  • CS Table Friday at noon: Law, Order, and Computers
  • More?

Upcoming Work

• Finish Homework 4.
• Look at the exam so that you have questions for Friday.
• Reading for Friday: Javadoc
• No writeup for inheritance lab.
• Still need to do writeup for polymorphism lab.

About Exam 1

• Four questions.
• Amaznigly fun.
• Sam will try to do the exam to.
• Sam will post unit tests for problems 3 and 4.

Questions on the Homework

Questions on inheritance and polymorphism

Why use interfaces when I can just use inheritance?

What if you want to support two different interfaces?

Images are renderable

Images are multipliable

And multiple inheritance is really confusing. What if both superclasses have a method with the same signature? (implementing multiple inheritance is also a PITN)

Arrays are probably Iterable, Clonable, and Comparable

There's not much data or methodology you'd want to inherit

If my class extends a class that implements multiple interfaces, does my class also implement those interfaaces?

Yes, and you don't even need to say so explicitly. (I hope.)

How do I use inheritance in place of interfaces?

We've seen that if A implements B then we can use A in place of B.

It's also the case that if A extends B then we can use A in place of B.

What are the big differences between inheritance and implementation?

In inheritance, you get copies of the fields and methods.

In inheritance, you need to be careful in the design of your constructors (see lab for details)

Lab

Thinking about ways to group blocks

TextBlock block1 = new TextBlock("Hello");
BoxedBlock block2 = new BoxedBlock(block1);

vs.

TextBlock block1 = new TextBlock("Hello");
TextBlock block2 = new BoxedBlock(block1);

vs.

TextBlock block2 = new BoxedBlock(new TextBlock("Hello"));

Problem 7

• How do I implement width?
  
  • What is the width of this object in terms of the width of the enclosed object?
• How do I implement height?
  • What is the width of this object in terms of the height of the enclosed object?
• What does the ith row look like?
  • Which row of the enclosed object?
  • How do we modify that row?