Interface Segregation Principle in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Interface Segregation Principle (ISP)

Which statement best describes the Interface Segregation Principle?

A Interfaces should be merged to reduce the number of classes in a system.

B All classes should implement a single large interface to ensure consistency.

C Interfaces should only be used for database access layers.

D Clients should not be forced to depend on interfaces they do not use.

💡 Hint

Think about how interfaces affect client dependencies and code flexibility.

The Interface Segregation Principle states that clients should not be forced to depend on interfaces they do not use. This promotes smaller, more specific interfaces rather than large, general ones.

❓ Architecture

intermediate

Applying ISP in a Payment System

You are designing a payment system with multiple payment methods: CreditCard, PayPal, and Bitcoin. Which design best follows the Interface Segregation Principle?

A Create a single interface IPayment with a generic pay() method that all payment classes implement.

B Do not use interfaces; implement payment methods directly in one class.

C Create separate interfaces for each payment method: ICreditCardPayment, IPayPalPayment, IBitcoinPayment. Each payment class implements only the relevant interface.

D Create one large interface IPayment with methods: payWithCreditCard(), payWithPayPal(), payWithBitcoin(). All payment classes implement all methods.

💡 Hint

Consider how to avoid forcing classes to implement methods they don't need.

ISP encourages creating smaller, specific interfaces so classes implement only what they need. Separate interfaces for each payment method avoid unnecessary dependencies.

❓ scaling

advanced

Scaling a Notification System with ISP

A notification system supports Email, SMS, and Push notifications. As the system grows, which approach best supports scalability and follows ISP?

A Use one interface INotification with methods sendEmail(), sendSMS(), sendPush(). All notification classes implement all methods.

B Create separate interfaces IEmailNotification, ISMSNotification, IPushNotification. Notification classes implement only the interfaces they support.

C Implement all notification methods in a single NotificationManager class without interfaces.

D Use a single interface with a send(type, message) method handling all notification types.

💡 Hint

Think about how adding new notification types affects existing classes.

Separate interfaces allow adding new notification types without changing existing classes, supporting scalability and adhering to ISP.

❓ tradeoff

advanced

Tradeoffs of Interface Segregation Principle

What is a common tradeoff when applying the Interface Segregation Principle in system design?

A It can increase the number of interfaces, making the system more complex to manage.

B It forces all clients to depend on a single large interface, reducing flexibility.

C It eliminates the need for interfaces, simplifying the codebase.

D It requires all classes to implement every method, increasing code duplication.

💡 Hint

Consider the balance between interface size and system complexity.

While ISP improves modularity, it can lead to many small interfaces, which may increase management overhead.

❓ component

expert

Identifying ISP Violation in Code Components

Given a system with a Printer interface having methods print(), scan(), fax(), and a class BasicPrinter implementing all methods but only supporting print(), what problem does this design illustrate?

A Violation of Interface Segregation Principle because BasicPrinter depends on methods it does not use.

B Correct use of ISP because all methods are in one interface.

C Violation of Single Responsibility Principle because BasicPrinter does too many things.

D No problem; this is standard interface design.

💡 Hint

Think about whether classes should implement methods they don't support.

BasicPrinter implementing unused methods violates ISP because it depends on methods it does not need, leading to unnecessary complexity.