UML +类图-在线电影租赁

Question

Create an object-oriented design for a streaming movie rental system (like NetFlix). The names of your classes, private instance variables, methods etc. are totally up to you.

Specifcation

Every user has the following information associated with them:

1. A name.
2. An account number.
3. An ordered playlist of movies.
   • In particular, if movie A is before movie B in the playlist, then the user watches A before B.
4. The five most recent movies that the user has watched.

There are three different kinds of users:

1. Trial
   • A trial user can only have one movie in their playlist at a time.
2. Members
   • A member can have up to 5 movies in their playlist at a time.
3. VIP Members
   • A VIP member can have an unlimited number of movies in their playlist.

Every user must be able to do the following operations:

1. Check-out a movie
   • If a user checks out a movie, then it is put at the end of the user's playlist.
2. Watch a movie
   • If a user watches a movie, then the movie is removed from the user's playlist. You may assume that the user can only watch whatever movie is at the front of the playlist.
3. Recall the five most recent movies that they have watched
   • This operation should print the most recent movies that the user has watched to the screen.

Every movie contains the following information:

1. A title
2. A date
3. A genre
4. A rental price

Notice that different users have different movie rental rights, so it is possible that a user will attempt to do something that (s)he is not allowed to do. When this occurs, you must do the following:

1. Make sure that the operation is not performed.
2. Print an informative error message that states why the operation could not be performed.

Your object-oriented design must include the following object-oriented features:

1. An abstract class
   • What should be the base class that other classes build of?
2. Inheritance
   • In particular, you must inherit from a base abstract class.
3. Polymorphism (Dynamic Binding)
   • In particular, your method for checking a movie out must be polymorphic.

I have come up with the following class diagram, which is not yet completed:

to start with I am little confused about where the three functionalities should go... check out the movie, watch a movie and get the last 5 recent watched movies. Also, Would like to know how to relate these classes.

I have edited my class diagram.. I am looking for some feedback on relationship of the classes

Answer 1

I'll give you a bit of direction on the abstract class part of this. You have correctly understood that User is an abstract class, and that your concrete classes inherit from it. However, you do not need to have an attribute that explains what type of user a given instance is. Call your concrete classes NormalUser, TrialUser, VIPUser. Make checkOut an abstract operation in your User class; since each concrete class handles this operation differently, you'll need to implement it in each class rather than in the User class. (The User class will directly implement those operations that each class does in the same way, such as getHistory.)

The polymorphism bit is that you declare a class of type User and instantiate it as one of the concrete subclasses. Then, when you call the checkOut method, you will get the varying behavior you've implemented in the subclasses.

I'll also give you some syntax correction:

Don't write "Concrete Class" in your concrete class labels, and don't put an «Abstract Class» stereotype in your abstract class label. The way that UML shows a class to be abstract is to italicize the title. That's all the distinction you need.

Don't put a «Class» stereotype on your classes. Stereotypes are to define a particular type of class such as «Utility».

Don't write «Stereotype» on your class labels for the same reason. There's no such stereotype already defined, and as Thomas Kilian says, a "stereotype" stereotype makes absolutely no sense so there's no reason to create one yourself.