Liskov Substitution Principle in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Liskov Substitution Principle (LSP)

Which of the following best describes the Liskov Substitution Principle in system design?

A Base classes must be replaceable by their derived classes without altering the correctness of the program.

B Base classes must never be extended by derived classes to avoid complexity.

C Subclasses should always add new methods instead of modifying existing ones.

D Derived classes can override base class methods with completely different behaviors.

💡 Hint

Think about substituting objects in a program without breaking it.

LSP states that objects of a superclass should be replaceable with objects of a subclass without affecting the program's correctness.

❓ Architecture

intermediate

Applying LSP in Class Hierarchies

Consider a class hierarchy where a Rectangle class has a method setWidth and setHeight. A subclass Square overrides these methods to keep width and height equal. Which problem does this violate according to LSP?

A No violation; LSP only applies to interfaces, not classes.

B Square perfectly follows LSP because it inherits Rectangle methods.

C Rectangle violates LSP because it allows width and height to be set separately.

D Square cannot be substituted for Rectangle because it changes expected behavior of setting width and height independently.

💡 Hint

Think about whether the subclass changes the expected behavior of the base class methods.

The Square class changes the behavior of setting width and height independently, breaking the expectation from Rectangle, thus violating LSP.

❓ scaling

advanced

Scaling Systems with LSP-Compliant Components

When designing a large-scale system with multiple service components, how does adhering to LSP help in scaling and maintaining the system?

A It forces all components to be identical, reducing flexibility in scaling.

B It ensures components can be replaced or extended without breaking existing integrations, easing scaling and maintenance.

C It requires rewriting all components when scaling to maintain consistency.

D It limits the number of components to avoid complexity.

💡 Hint

Consider how substitutability affects system upgrades and extensions.

Adhering to LSP allows components to be replaced or extended without breaking existing contracts, which supports easier scaling and maintenance.

❓ tradeoff

advanced

Tradeoffs When Enforcing LSP Strictly

What is a common tradeoff when strictly enforcing LSP in a complex system design?

A It forces all subclasses to have identical code, causing duplication.

B It always increases system complexity and bugs.

C It may limit the ability to optimize subclasses for specific cases, reducing performance gains.

D It eliminates the need for interfaces and abstract classes.

💡 Hint

Think about balancing design purity and practical optimizations.

Strict LSP enforcement can restrict subclasses from changing behavior to optimize for special cases, potentially limiting performance improvements.

❓ component

expert

Identifying LSP Violation in Component Interaction

Given a payment processing system where a PaymentProcessor interface defines a method processPayment(amount). A subclass CryptoPaymentProcessor overrides this method but throws an exception if the amount is below a minimum threshold, unlike the base implementation which accepts all amounts. What is the impact of this on LSP?

A CryptoPaymentProcessor violates LSP because it changes the expected behavior by throwing exceptions for inputs accepted by the base class.

B CryptoPaymentProcessor follows LSP because it extends the base interface and adds validation.

C There is no impact on LSP since exceptions are allowed in subclasses.

D LSP is not applicable to interfaces, only to concrete classes.

💡 Hint

Consider whether the subclass can be used anywhere the base class is expected without causing errors.

The subclass throws exceptions for inputs that the base class accepts, breaking substitutability and violating LSP.