README for the abstract factory example by Professor Futrelle
For COM1204, July 14, 2002.

The key point of this example can be seen in the file AbstractFactoryTest.java.
The lines below are numbered for discussion.

Line 17 shows that theTrip is of class (type) DogShoppingTrip.
But in lines 23 and 34, two distinct subclasses of DogShoppingTrip
are returned, LittleDogShoppingTrip at line23 and BigDogShoppingTrip
at line 34.  Look at the TripFactory class to see how this is done;
the source, TripFactory.java, is short and simple.

Once the appropriate subclass is returned, the three objects are
obtained from theTrip, of classes Dog, DogHouse and DogFood.
But depending on what type of shopping trip is being used, 
the instances are different, having different values of an internal
descriptor in each.  This is because, for example, buyDog() exists
in two variants. One of them can be found in BigDogShoppingTrip 
and has the definition:

	Dog buyDog(){
		return new Dog("BIG!");
		}

There are five additional function definitions to handle the three functions
variants in each of the two subclasses.  You can see them for yourself.

So that's how this example works.  It contains seven classes plus a 
testing class:

  Dog.java
  DogHouse.java
  DogShoppingTrip.java
  DogFood.java
  BigDogShoppingTrip.java
  AbstractFactoryTest.java
  LittleDogShoppingTrip.java
  TripFactory.java

In class, we'll discuss some of the alternatives to this approach
which don't work as well, to help recommend the use of the abstract
factory, when it's appropriate.
  
I hope this example helps you.

 -- Professor Futrelle


1 /**
2   * This is to demonstrate abstract  factory classes.
3   *
4   * @author Bob Futrelle
5   * @version 1.0 7/12/2002
6   *
7   */
8  
9   public class AbstractFactoryTest  {
10 
11 	
12 	public static void main(String[] args) {
13 	
14 		Dog dog;
15 		DogHouse dogHouse;
16 		DogFood dogFood;
17 		DogShoppingTrip theTrip;
18 		
19 		// Create the factory
20 		TripFactory trips = new TripFactory();
21 		
22 		// Get a little dog shopping trip
23 		theTrip = trips.getTrip(DogShoppingTrip.LITTLE);
24 		
25 		say("Here's the info for the little dog shopping excursion:\n");
26 		dog = theTrip.buyDog();
27 		dog.speak();
28 		dogHouse = theTrip.buyDogHouse();
29 		dogHouse.describe();
30 		dogFood = theTrip.buyDogFood();
31 		dogFood.describe();
32 		
33 		// Get a BIG DOG shopping trip		
34 		theTrip = trips.getTrip(DogShoppingTrip.BIG);
35 		
36 		say("\nHere's the info for the BIG DOG shopping excursion:\n");
37 		// Note: code below is the same as the above
38 		dog = theTrip.buyDog();
39 		dog.speak();
40 		dogHouse = theTrip.buyDogHouse();
41 		dogHouse.describe();
42 		dogFood = theTrip.buyDogFood();
43 		dogFood.describe();
44 		
45 		
46 	} // main()
47 	
48 	static void say(String s) {
49 		System.out.println(s);
50 		}
51 }