1. Design Patterns

2. Video Rental System Rental of each movie is determined by the type.
VideoDescription
barCode
title
type
…….. 1 *
Member
Rental *
name
address
phoneNumber
creditCard#
Address
userName
password
rentalStore
rentalDate
dueDate
returnDate
returnTime
VideoCopy * *
rents
copyID
request
Rental of each movie is determined by the type.
There are currently in the system three types of movies
New releases have a rental fee of $3.00
Children’s movies rent for $1.00
All other movies rent for $2.00

3. Video Rental System
VideoDescription
barCode
title
type
…….. 1 *
Member
Rental *
name
address
phoneNumber
creditCard#
Address
userName
password
rentalStore
rentalDate
dueDate
returnDate
returnTime
VideoCopy * *
rents
copyID
request
In design you realized you realized you needed a method to make the statement to for the rentals…(you might have placed it in MEMBER or the use case class RENTVIDEO
While other code would be present, there would be a method that calculates the cose of the movie depending on the days and the price of the movie
There would be a switch or case statement to select the price depending on the type

4. Video Rental System public Void makeStatement () {
int price = 0, total = 0, int days
Iterator videos = rents.iterator();
…..
while (videos.hasNext()) {
Rental rents = (Rental) videos.next();
int type = rents.getMovie().getType();
switch (type) {
case Movie.REGULAR: price = 200; break;
case Movie.NEWRELEASE: price = 300; break;
case Movie.CHILDREN: price = 100; break;
days = computeDays(rentalDate);
cost = days * price;
}……..

5. Make this a method called computeCost
Video Rental System
public Void makeStatement () {
int price = 0, total = 0
Iterator videos = rents.iterator();
…..
while (videos.hasNext()) {
Rental rents = (Rental) videos.next();
int type = rents.getMovie().getType();
switch (type) {
case Movie.REGULAR: price = 200; break;
case Movie.NEWRELEASE: price = 300; break;
case Movie.CHILDREN: price = 100; break;
days = computeDays(rentalDate);
cost = days * price;
Make this a method called computeCost
During design we recognized we would need an algorithm to compute the days of the rental….
We assume no overdues for simplicity of our example
So…. We make a method (not specified here)
We then use that method to compute cost based on price
But this needs to be a method of its own…..

6. Video Rental System public Void makeStatement () {
int price = 0, total = 0
Iterator videos = rents.iterator();
…..
while (videos.hasNext()) {
Rental rents = (Rental) videos.next();
int type = rents.getMovie().getType();
switch (type) {
case Movie.REGULAR: price = 200; break;
case Movie.NEWRELEASE: price = 300; break;
case Movie.CHILDREN: price = 100; break;
days = computeDays(rentalDate);
cost = days * price;
Now it is a method that returns the cost of the rental and should probably be placed in the RENTAL CLASS
Rental
rentalStore
rentalDate
dueDate
returnDate
returnTime
computeDays
computeCost
Then we realize that this method is misplaced

7. Video Rental System public Void makeStatement () {
int price = 0, total = 0
Iterator videos = rents.iterator();
…..
while (videos.hasNext()) {
Rental rents = (Rental) videos.next();
int type = rents.getMovie().getType();
switch (type) {
case Movie.REGULAR: price = 200; break;
case Movie.NEWRELEASE: price = 300; break;
case Movie.CHILDREN: price = 100; break;
days = computeDays(rentalDate);
cost = days * price;
BUT: getCost uses type from from the MovieDescription to decide the price. We could pass the days to MovieDescription and have it select the price since it has the type.
VideoDescription
barCode
title
Type
getCost (days)
……..
Then we realize it is still not in the right place

8. Video Rental System public Void makeStatement () {
int price = 0, total = 0
Iterator videos = rents.iterator();
…..
while (videos.hasNext()) {
Rental rents = (Rental) videos.next();
int type = rents.getMovie().getType();
switch (type) {
case Movie.REGULAR: price = 200; break;
case Movie.NEWRELEASE: price = 300; break;
case Movie.CHILDREN: price = 100; break;
days = computeDays(rentalDate);
cost = days * price;
Still: getCost currently are not exploiting dynamic binding to make the case decisions
==> sub-classing of three different sub-types: Regular, NewRelease, and Children would allow this
VideoDescription
A better design but an opportunitiy for a pattern may be here
Regular
Children
NewRelease

9. Video Rental System
VideoDescription
barCode
title
type
……..
The strategy pattern is certainly in order when you are basing behavior on a type.
Regular
Children
NewRelease
getCost
getCost
getCost
NOTE: even more flexibility can be achieved if the class model is developed further to a framework by applying a construct like the Strategy Pattern.

10. Video Rental System
9. step -> additional flexibility by adding a class Price responsible for the pricing strategy acting as framework hot-spot
VideoDescription
barCode
title
type
……..
Price
getCost
During design we recognized we would need an algorithm to compute the days of the rental….
We assume no overdues for simplicity of our example
So…. We make a method (not specified here)
We then use that method to compute cost based on price
But this needs to be a method of its own…..
Regular
Children
NewRelease
getCost
getCost
getCost
So we add a class responsible for the pricing strategy……

11. Video Rental System abstract class Price {
public abstract int getCost (int days); }
class Regular extends Price {
public int getCost (int days) {
return days * 200;
class NewRelease extends Price {
public int getCost (int days) { return days * 300; }
class Children extends Price {
return days * 100;
…..
Then we realize it is still not in the right place

12. Video Rental System class MovieDescription { private String title; …….
private Price pricing;
…..
public Price getPrice () { return price; } ….
public int getCharge (int days) { return pricing.getCost(days); } }
Then we realize it is still not in the right place

13. Video Rental System class Rental { private MovieDescription movie;
private int days; ….
public Movie getMovie () { return movie; }
public int computeDays () { …..return days; }
public int getCost () { return movie.getCost(days); } }
Then we realize it is still not in the right place