POO TV

Copyright 2022 Toaca Alexandra Simona

Implementation

Entry Point

Streaming Service Class

• Contains the start method which handles actions
• Stores the state of the StreamingService (current user, current page, etc)
• The getters and setters are static because this class needs to be modified internally from multiple places in the program
• I did not make it a singleton because every time I create a new instance it clears the old one. If I made it a Singleton I would have needed a clear() method

Storing the input

Database Class

• This is implemented as a Singleton to be accessed from anywhere in the program
• Contains the users registered and the movies available on the platform

I/O

InputHandler Class

• Loads the JSON text input into an Input object
• Loads the users and movies from Input into the Database loadInputIntoDatabase
• the getActions method uses an ActionFactory to return the actions as proper objects -> used for the Visitor pattern explained later

OutputWriter Class

• Writes the output to a file in JSON format
• Adds a new objectNode (containing an Output object) to an output ArrayNode
• The ArrayNode is written to the output file as JSON at the end of the program

Actions and Pages

• There are classes for every type of page and action, each having a base class Page or Action
• An action is permitted only on certain pages, an invalid action producing an error -> I used a modified Visitor pattern to have a default behavior for the actions (error) and then overriding it for the cases in which the action is permitted.
• The construction in the entry point is as follows: currentPage.accept(action)
• Pages are visited by Actions
• The correct behavior of the action is selected at runtime depending on the current page
• Also, an action has access to the page it was called on without checking what page the user is on (for example, in ChangePageAction, we check if the next page is a valid sub page of the current page by using page.getSubPages(), referring automatically to the page the action was called on).

Notification system

• used the Observer design pattern to notify users when a movie is added to/deleted from the database.
• The users are the observers and the database is observable
• By subscribing to a genre, a user is added as an observer and the update function handles whether the notification will be relevant or not to the user (the genre of the movie is one the user subscribed to)

Recommendations

RecommendationGenerator class

• computes the number of likes that every movie genre got
• creates a list of the genres in descending order by number of likes
• searches through the unwatched movies in the database for a recommendation
• returns the notification containing the recommendation for the user