Composition over inheritance in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why prefer composition over inheritance?

Which of the following best explains why composition is often preferred over inheritance in system design?

A Inheritance avoids code duplication better than composition in every scenario.

B Composition allows changing behavior at runtime by swapping components, while inheritance fixes behavior at compile time.

C Composition requires fewer classes than inheritance in all cases.

D Inheritance always leads to faster code execution than composition.

💡 Hint

Think about flexibility and how behavior can be changed after the system is running.

Composition allows objects to contain other objects and change their behavior dynamically by swapping components. Inheritance fixes behavior in a class hierarchy, making it less flexible.

❓ Architecture

intermediate

Design choice for a payment system

You are designing a payment system that supports multiple payment methods (credit card, PayPal, crypto). Which design approach best uses composition over inheritance?

A Use inheritance to create subclasses for each payment type and hardcode the payment logic in each subclass.

B Create a PaymentMethod interface and have each payment type inherit from it, implementing their own logic.

C Create separate classes for each payment type with no shared interface or composition.

D Create a PaymentProcessor class that contains a PaymentMethod component which can be swapped to change payment type at runtime.

💡 Hint

Consider how you can change payment methods without changing the main processor class.

Using composition, the PaymentProcessor contains a PaymentMethod component that can be swapped dynamically, allowing flexible payment method changes without modifying the processor.

❓ scaling

advanced

Scaling a notification system with composition

You have a notification system that sends alerts via email, SMS, and push notifications. To scale and add new channels easily, which design is best?

A Use composition where a NotificationSender class contains a list of NotificationChannel components that can be added or removed dynamically.

B Hardcode all notification types inside one large Notification class using if-else statements.

C Use inheritance to create subclasses for each notification type and add new subclasses for new channels.

D Create separate monolithic services for each notification type without shared components.

💡 Hint

Think about how to add or remove notification channels without changing existing code.

Composition allows the NotificationSender to hold multiple NotificationChannel components, making it easy to add or remove channels dynamically and scale the system.

❓ tradeoff

advanced

Tradeoffs between composition and inheritance

Which of the following is a valid tradeoff when choosing composition over inheritance?

A Inheritance always results in simpler code and fewer classes than composition.

B Composition does not allow code reuse, unlike inheritance which always does.

C Composition can increase the number of objects and indirection, potentially impacting performance compared to inheritance.

D Inheritance allows changing behavior at runtime, while composition fixes behavior at compile time.

💡 Hint

Consider the overhead of managing multiple objects versus a class hierarchy.

Composition can introduce more objects and layers of delegation, which may add some performance overhead compared to inheritance's direct method calls.

❓ component

expert

Component interaction in a compositional design

In a compositional design for a media player, the Player class composes components: Decoder, Renderer, and Logger. Which sequence best describes the request flow when playing a media file?

A 1, 2, 3, 4

B 1, 3, 2, 4

C 2, 1, 3, 4

D 1, 4, 2, 3

💡 Hint

Think about the logical order of processing from request to output and logging.

The Player first receives the request, then the Decoder processes the file, Renderer outputs the media, and Logger records the event last.