Section outline

• Classes Relationships
  

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  Object-oriented programming (OOP) is a powerful approach to software design and development. At the heart of OOP are some relationships between classes. These relationships help in modeling complex systems effectively and build robust, maintainable, and scalable software applications.

  Studying and understanding OOP class relationships is essential. As:

  Well-defined class relationships can improve the overall maintainability of the codebase by reducing coupling, increasing cohesion, and making it easier to understand and modify the system.

  The choice of class relationships can impact the performance and efficiency of the system, as certain relationships may be more suitable for specific use cases or requirements.

  Class relationships affect the testability of the system, as they impact the way classes can be isolated and tested independently.

  In this course, we will dive into these relationships, exploring when and how to apply them.

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    Quiz

    Let's think!!! Quiz

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• Inheritance Relationship
  
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    Class Relationship - Inheritance Video Time

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    Class Relationship - Inheritance In Java Video Time

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• Aggregation and Composition
  
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    Class Relationship - Composition Video Time

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    Class Relationship - Aggregation Video Time

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• Override - Overload
  
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    Override - Overload Video Time

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• Exercise Time
  
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    Exercise 1: Designing a Vehicle Management System

    Imagine you are tasked with designing an Object-Oriented Vehicle Management System. This system should be able to manage various types of vehicles, their characteristics, and their operations.

    Your task is to design the class hierarchy and inheritance relationships for this system.

    Steps:

    1. Identify the key vehicle types: Start by identifying the main types of vehicles that you need to manage in the system, such as Cars, Motorcycles, Trucks, and Bicycles.

    2. Analyze the common characteristics and behaviors: Examine the common characteristics and behaviors shared among the different vehicle types. For example, all vehicles have properties like make, model, and year, and they can all be started, stopped, and moved.

    3. Design the inheritance hierarchy:

       • Create a base Vehicle class that encapsulates the common characteristics and behaviors.
       • Derive subclasses from the Vehicle class for each specific vehicle type (e.g., Car, Motorcycle, Truck, Bicycle).
       • Ensure that the subclasses inherit the appropriate properties and methods from the Vehicle class.
       • Identify any additional properties or methods that are specific to each vehicle type and add them to the respective subclasses.

    4. Implement the classes:

       • Create the Vehicle class and define its properties and methods.
       • Implement the subclasses (e.g., Car, Motorcycle, Truck, Bicycle) and ensure that they inherit from the Vehicle class.
       • Add any additional properties and methods specific to each vehicle type.

    5. Test the inheritance hierarchy:

       • Create instances of the different vehicle types and verify that they can access the inherited properties and methods from the Vehicle class.
       • Ensure that any specialized properties and methods added to the subclasses are functioning as expected.

    6. Extend the hierarchy:

       • Identify any additional vehicle types that could be added to the system (e.g., Electric Vehicles, Hybrid Vehicles).
       • Design the appropriate subclasses and integrate them into the existing inheritance hierarchy.
       • Ensure that the new subclasses inherit the necessary properties and methods from the Vehicle class and add any additional specialized functionality.

    7. Evaluate the design:

       • Assess the reusability and extensibility of the system. How easy would it be to add new vehicle types in the future?
       • Consider the maintainability of the codebase. How clear and understandable is the inheritance hierarchy?
       • Examine the testability of the system. How easily can individual classes be tested in isolation?
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    Exercise 2: Designing a Video Game System

    Imagine we are building a video game system with different types of games and players.

    1. Inheritance:

       • Create a base Game class that defines common properties and methods for all games, such as the game title, genre, and a method to start the game.
       • Create subclasses of Game to represent different game genres, such as ActionGame, PuzzleGame, and RPG.

    2. Composition:

       • Create a Player class that has a name property and a playGame method that takes a Game object as a parameter and starts the game.
       • The Player class should have a Inventory class as a member, which can hold various game items.

    3. Aggregation:

       • Create a GameLibrary class that can hold a collection of Game objects. The GameLibrary class should have methods to add, remove, and retrieve games.
       • The Player class should have a GameLibrary object as a member, allowing the player to access and play the games in their library.

    4. Method Overloading:

       • In the Inventory class, create a addItem method that can accept different types of items, such as weapons, armor, or consumables. Overload the addItem method to handle the different item types.

    5. Method Overriding:

       • In the ActionGame, PuzzleGame, and RPG classes, override the start method from the base Game class to provide game-specific implementation.
       • For example, the ActionGame class might have a different game start sequence compared to the PuzzleGame class.
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    Exercise 3: Designing a Library Management System

    1. Inheritance:

       • Create a base LibraryItem class that defines common properties and methods for all library items, such as the title, author, and a method to check out the item.
       • Create subclasses of LibraryItem to represent different types of library items, such as Book, Magazine, and AudioBook.

    2. Composition:

       • Create a Patron class that has a name property and a checkOutItem method that takes a LibraryItem object as a parameter and checks out the item.
       • The Patron class should have a CheckoutHistory class as a member, which can keep track of the items the patron has checked out.

    3. Aggregation:

       • Create a Library class that can hold a collection of LibraryItem objects. The Library class should have methods to add, remove, and retrieve library items.
       • The Patron class should have a Library object as a member, allowing the patron to access and check out items from the library.

    4. Method Overloading:

       • In the CheckoutHistory class, create a recordCheckout method that can accept different types of library items, such as books, magazines, and audiobooks. Overload the recordCheckout method to handle the different item types.

    5. Method Overriding:

       • In the Book, Magazine, and AudioBook classes, override the checkOut method from the base LibraryItem class to provide item-specific implementation.
       • For example, the AudioBook class might have a different check-out process compared to the Book class.