Name:
(as it would appear on official course roster)
Umail address:	@umail.ucsb.edu	section 4pm,5pm,6pm
Optional: name you wish to be called if different from name above.
Optional: name of "homework buddy" (leaving this blank signifies "I worked alone"

h03: HFJ 7, 8: Inheritance, Polymorphism, Abstract Classes

ready?	assigned	due	points
true	Mon 04/22 05:00PM	Mon 04/29 05:00PM

You may collaborate on this homework with AT MOST one person, an optional "homework buddy".

MAY ONLY BE TURNED IN IN THE LECTURE/LAB LISTED ABOVE AS THE DUE DATE,
OR IF APPLICABLE, SUBMITTED ON GRADESCOPE. There is NO MAKEUP for missed assignments;
in place of that, we drop the two lowest scores (if you have zeros, those are the two lowest scores.)

Reading Assignment:

Read HFJ Chapter 7 and HFJ Chapter 8, along with the online reading notes that go with those chapters. Then, do the problems below. Refer back to previous chapters as needed.

(10 pts) Please fill in the information at the top of this homework sheet, including your name and umail address. Put the time your discussion section starts (4pm,5pm,6pm) in the space indicated (the one you are registered for—even if you usually attend a different one.) If the other two items apply, please fill them in as well. Please do this every single time you submit homework for this class.

(10 pts) Based on your reading in HFJ Chapter 7, complete the following exercise from p. 179, putting a check next to the relationships that make sense.

✓	__ extends __
	Oven extends Kitchen
	Guitar extends Instrument
	Person extends Employee
	Ferrari extends Engine
	FriedEgg extends Food

✓	__ extends __
	Beagle extends Pet
	Container extends Jar
	Metal extends Titanium
	GratefulDead extends Band
	Beverage extends Martini

Note: The Grateful Dead is a band from the 1960s, and a beagle is a type of dog.

Note to grader: subtract 2 for each incorrect answer, with a minimum grade of zero.

(10 pts) Based on your reading in HFJ Chapter 7:

What does it mean to have a “polymorphic argument” or a “polymorphic return type” for a method? Explain with an example—but NOT using the example of Vets and Animals used in the book. Substitute your own example. Give a detailed enough description of the class hierarchy you have in mind to make it clear that you get the concept.
Java code examples

Several questions on this page ask you to illustrate your answers with Java code excerpts.

Your examples do not need to be a “complete” Java classes. They can be partial Java classes with with some ellipsis (…) to show parts you are leaving out. It needs to have just enough detail to illustrate the point you are making. For example the following Java code might be used to illustrate various things (what those are is left for you to figure out.)
```
public class Bar { ... }
public class Baz { ... }
public class Foo extends Bar {
  private Baz thingy;
  ...
}
```
(10 pts) Based on your reading in HFJ Chapter 8:

Briefly describe the difference between an abstract class and an interface.
(10 pts) What is one advantage of using an ArrayList over a plain old Java array (e.g. ArrayList<Integer> nums; vs. int [] nums;)?
Two terms that are very important, and commonly confused are *overloading* vs. *overriding*. There is a passage in HFJ Chapter 7 that helps to explain the difference.
1. (10 pts) Explain what overloading is, with a specific example of Java code.
2. (10 pts) Explaing what overriding is, with a specific example of Java code.
There is a passage in HFJ Chapter 7 that helps to explain the difference between IS-A and HAS-A:
1. (5 pts) Which one corresponds to composition?
2. (5 pts) Which one corresponds to inheritance?
3. (10 pts) Explain (with some Java code) an example of two classes that have a HAS-A relationship.
(10 pts) Why do some classes in the Java API have package names that start with java.blah while others have package names that start with javax.blah? What does the x mean?

h03: HFJ 7, 8: Inheritance, Polymorphism, Abstract Classes

Java code examples