COM1204 Summer Quiz #1 Version A- Prof. Futrelle

Quiz #1 - Thursday 3 July - Closed book/notes

Be sure to write complete information in your blue exam book: Name, course, date, exam version A.

Question 1: You are given the following test program for reference:

class TestDogs {
	public static void main(String[] args) {
		Kennel kennelA = new KennelA();
		Kennel kennelB = new KennelB();
		Barker dogA = kennelA.getADog();
		Barker dogB = kennelB.getADog();
		System.out.println(dogA.speak() + " " + dogB.speak());
	}
	// Output of the above is: "WOOOF! yip"
}

You are to write the following code, all with public access. (Hint: The classes in which methods are implmented are related to the corresponding interfaces.)

• The interface Barker with the String valued speak() of no arguments.
• The classes BigDog and LittleDog that implement speak() to return "WOOF!" and "yip", respectively.
• The interface Kennel with the Barker valued getADog() of no arguments.
• The classes KennelA and KennelB that implement getADog() to return a new BigDog and a new LittleDog, respectively.

The hallmarks of the Factory Method are that an operation:

• Creates a new object.
• Returns a type that is an abstract class or an interface.
• Is implemented by several classes.

Using careful technical terms, discuss the above three points as they apply to the method getADog(). As part of this explain why dogA.speak() and dogB.speak() return distinct results. Hint: Discuss the apparent and actual types of dogA and dogB.

Question 2: The general structure of the Observer pattern as specified in your textbook, and some specifics of the "Gossip" example I have previously given you are paired below. Your job is to explain the correspondence in each pair.

• Subject/Space
  • The Subject can attach an Observer and notify Observers.
  • How does the corresponding Space component function in Gossip?
  
  
• Observer/TalkerListener
  • The Observer can register with a Subject and update the Subject.
  • How does the corresponding TalkerListener component function in Gossip?