Single Responsibility Principle in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the Single Responsibility Principle Violation

Which of the following class designs violates the Single Responsibility Principle (SRP)?

A A class dedicated solely to formatting reports.

B A class responsible only for logging system events.

C A class that only manages database connections.

D A class that handles user authentication and also sends email notifications.

💡 Hint

SRP means a class should have only one reason to change.

Option D mixes two responsibilities: authentication and email notifications, violating SRP. Other options have a single responsibility.

❓ Architecture

intermediate

Refactoring for Single Responsibility Principle

You have a class that manages both user data validation and user data storage. How should you refactor it to follow SRP?

A Split the class into two: one for validation and one for storage.

B Keep the class as is but add more methods for other user operations.

C Remove validation and only keep storage in the class.

D Merge the class with another class that handles user interface.

💡 Hint

Think about separating concerns into distinct classes.

Splitting responsibilities into separate classes ensures each class has one reason to change, following SRP.

❓ scaling

advanced

Scaling Impact of Violating Single Responsibility Principle

What is a likely consequence of violating SRP in a large-scale system?

A Faster deployment due to fewer classes.

B Improved modularity and easier testing.

C Changes in one feature cause unexpected bugs in unrelated features.

D Reduced code duplication across modules.

💡 Hint

Consider how tightly coupled responsibilities affect maintenance.

Violating SRP causes classes to have multiple reasons to change, increasing risk of bugs when modifying one feature.

❓ tradeoff

advanced

Tradeoff of Strict Single Responsibility Principle Adherence

What is a potential downside of strictly applying SRP by creating many small classes?

A Increased complexity in managing many small classes.

B Reduced code readability due to fewer classes.

C Higher risk of duplicated code within classes.

D Less flexibility in changing individual components.

💡 Hint

Think about the overhead of many small parts in a system.

While SRP improves modularity, too many small classes can increase complexity in understanding and managing the system.

❓ component

expert

Determining Single Responsibility in a Microservice

A microservice handles user profile updates, notification sending, and analytics tracking. Which change best aligns it with SRP?

A Add caching to the existing microservice to improve performance.

B Split the microservice into three: one for profile updates, one for notifications, and one for analytics.

C Combine this microservice with the authentication microservice for better integration.

D Keep all features but separate them into different methods within the same microservice.

💡 Hint

SRP applies to services as well as classes.

Splitting the microservice by responsibility reduces coupling and aligns with SRP at the service level.

Practice

1. What does the Single Responsibility Principle (SRP) mean in simple terms?

easy

A. A class should handle multiple tasks to reduce the number of classes.

B. Each class or module should have only one job or responsibility.

C. All functions should be written in a single class for simplicity.

D. Classes should share responsibilities to improve collaboration.

Solution

1. Step 1: Understand the principle's core idea

   The Single Responsibility Principle states that a class or module should have one and only one reason to change, meaning it should do one job.

2. Step 2: Match the explanation to the options

   Each class or module should have only one job or responsibility. clearly states that each class or module should have only one job, which matches the principle.

3. Final Answer:

   Each class or module should have only one job or responsibility. -> Option B

4. Quick Check:

   Single Responsibility Principle = One job per class [OK]

Hint: One class, one job keeps code clean and simple [OK]

Common Mistakes:

• Thinking one class should do many tasks
• Believing all code should be in one place
• Confusing SRP with code reuse

2. Which of the following class names best follows the Single Responsibility Principle?

easy

A. UserAuthenticator

B. DataProcessorAndReportGenerator

C. UserManagerAndLogger

D. FileHandlerAndNetworkSender

Solution

1. Step 1: Analyze class names for single responsibility

   Classes with multiple responsibilities in their names violate SRP. UserManagerAndLogger, DataProcessorAndReportGenerator, and FileHandlerAndNetworkSender suggest multiple jobs.

2. Step 2: Identify the class with one clear responsibility

   UserAuthenticator clearly focuses on one task: authenticating users, which aligns with SRP.

3. Final Answer:

   UserAuthenticator -> Option A

4. Quick Check:

   Class name with one job = UserAuthenticator [OK]

Hint: Class name shows one clear job means SRP followed [OK]

Common Mistakes:

• Choosing classes with multiple jobs in name
• Ignoring SRP and mixing responsibilities
• Assuming longer names are better

3. Given this Python class, what is the main SRP violation?

class OrderProcessor:
    def process_order(self, order):
        self.validate_order(order)
        self.save_order(order)
        self.send_confirmation_email(order)

    def validate_order(self, order):
        pass

    def save_order(self, order):
        pass

    def send_confirmation_email(self, order):
        pass

medium

A. The class handles order validation, saving, and email sending, mixing responsibilities.

B. The class does not validate the order properly.

C. The class should not have any methods.

D. The class only processes orders and follows SRP.

Solution

1. Step 1: Identify responsibilities in the class

   The class OrderProcessor validates orders, saves orders, and sends confirmation emails. These are three distinct jobs.

2. Step 2: Check SRP compliance

   SRP requires one responsibility per class. Mixing validation, saving, and emailing violates SRP.

3. Final Answer:

   The class handles order validation, saving, and email sending, mixing responsibilities. -> Option A

4. Quick Check:

   Multiple jobs in one class = SRP violation [OK]

Hint: One class, one job; multiple jobs mean SRP broken [OK]

Common Mistakes:

• Ignoring multiple responsibilities in one class
• Thinking multiple methods mean multiple classes
• Assuming SRP allows all related tasks in one class

4. You have a class that both calculates taxes and generates invoices. What is the best way to fix this SRP violation?

medium

A. Combine tax calculation and invoice generation into a single method.

B. Add more methods to handle discounts and payments in the same class.

C. Split the class into two: one for tax calculation and one for invoice generation.

D. Remove tax calculation and keep only invoice generation.

Solution

1. Step 1: Identify the problem with the current class

   The class does two jobs: calculating taxes and generating invoices, which breaks SRP.

2. Step 2: Apply SRP by separating responsibilities

   Splitting into two classes, each with one responsibility, fixes the violation and improves maintainability.

3. Final Answer:

   Split the class into two: one for tax calculation and one for invoice generation. -> Option C

4. Quick Check:

   Separate classes for separate jobs = SRP fix [OK]

Hint: Split mixed jobs into separate classes to follow SRP [OK]

Common Mistakes:

• Adding unrelated methods to the same class
• Combining jobs into one method
• Removing needed functionality instead of splitting

5. You are designing a system for a library. Which design best follows the Single Responsibility Principle?

hard

A. A single class 'LibrarySystem' that manages books, users, loans, and notifications.

B. A single class 'Library' that handles everything including maintenance and reporting.

C. One class 'LibraryManager' that handles books and users, and another class 'LoanAndNotificationManager' for loans and alerts.

D. Separate classes: 'BookManager' for books, 'UserManager' for users, 'LoanManager' for loans, and 'NotificationService' for alerts.

Solution

1. Step 1: Analyze each design for responsibility separation

   Designs with a single class handling books, users, loans, and notifications, or a single class handling everything, put many jobs into one class, violating SRP. Designs with one class for books and users, and another for loans and notifications, mix multiple jobs in each class.

2. Step 2: Identify the design with clear single responsibilities

   Separate classes: 'BookManager' for books, 'UserManager' for users, 'LoanManager' for loans, and 'NotificationService' for alerts. separates concerns into distinct classes, each with one responsibility, following SRP best.

3. Final Answer:

   Separate classes: 'BookManager' for books, 'UserManager' for users, 'LoanManager' for loans, and 'NotificationService' for alerts. -> Option D

4. Quick Check:

   Separate classes for separate jobs = SRP followed [OK]

Hint: One class per job in system design follows SRP best [OK]

Common Mistakes:

• Grouping unrelated responsibilities in one class
• Mixing multiple jobs in fewer classes
• Ignoring SRP for convenience