h04: HFJ 7,8: Inheritance, Polymorphism, Abstract Classes, JN7 Ch2 pp.33-50.

Reading Assignment:

• Read and , along with the online reading notes that go with those chapters.

Also skim JN7 Ch2 pp. 33-50. While you should read the HFJ chapters carefully, in this case, pp. 33-50 can mostly be skimmed; they are primarily for reference and I want you to know where to turn in the book if you need that material. You should, however, make sure you understand the difference between associativy and precedence, and read carefully enough that you are able find the answers to the questions given.

Then, do the problems below. Refer back to previous chapters as needed.

1. (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 (5pm, 6pm, 7pm) 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.
2. (10 pts) Based on your reading in , 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.

3. (10 pts) Based on your reading in :

   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.

4. 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 :

   Briefly describe the difference between an abstract class and an interface.

5. (10 pts) What is one advantage of using an ArrayList over a plain old Java array (e.g. ArrayList<Integer> nums; vs. int [] nums;)?

6. Two terms that are very important, and commonly confused are *overloading* vs. *overriding*. There is a passage in 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.

7. There is a passage in 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?

8. From JN7 Ch3, pp. 33-50:

   1. (10 pts) Explain the difference between operator associativity and operator precedence

   2. (5 pts) How many levels of operator precedence are there in Java?

   3. (5 pts) In Java (also in C and C++) there is an operator with three operands (a “ternary” operator). The first operand must always be an expression of a specific type. What is this type?