COM1204 Summer Quiz #1 Version B - 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 B.

Question 1: 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?

Question 2: You are given the following test program for reference. (Hint: The classes in which methods are implmented are related to the corresponding interfaces.)

class TestCars {
	public static void main(String[] args) {
		Dealer DealerA = new DealerA();
		Dealer DealerB = new DealerB();
		Speed carA = DealerA.getACar();
		Speed carB = DealerB.getACar();
		System.out.println(carA.howFast() + " " + carB.howFast());
	}
	// Output of the above is: "FAST! Not so fast"
}

You are to write the following code, all with public access:

• The interface Speed with the String valued howFast() of no arguments.
• The classes FastCar and SlowCar that implement howFast() to return "FAST!" and "Not so fast", respectively.
• The interface Dealer with the Speed valued getACar() of no arguments.
• The classes DealerA and DealerB that implement getACar() to return a new FastCar and a new SlowCar, 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 getACar(). As part of this explain why carA.howFast() and carB.howFast() return distinct results. Hint: Discuss the apparent and actual types of carA and carB.