[Solved] Trace the sequence of events when a client calls a method on a subclass instance that violates the Liskov Substitution Principle by strengthening a postcondition. What happens step-by-step? | OOP & Design Patterns

OOP & Design Patterns - Liskov Substitution Principle - Subtype Behavioural Contract

Trace the sequence of events when a client calls a method on a subclass instance that violates the Liskov Substitution Principle by strengthening a postcondition. What happens step-by-step?

AThe client receives a result that meets the superclass contract, so no issues arise.

BThe subclass method returns a stricter result than expected, potentially causing client failures.

CThe client silently ignores the stricter postcondition, so behavior is unaffected.

DThe subclass method throws an exception due to the strengthened postcondition.

Step-by-Step Solution

Step 1: Recall LSP postcondition rule
Subclasses must not strengthen postconditions; they can only maintain or weaken them.
Step 2: Trace client call
The client expects results conforming to the superclass contract. If subclass returns stricter results, some clients expecting broader results may fail.
Step 3: Analyze options
The subclass method returns a stricter result than expected, potentially causing client failures. correctly identifies potential client failures due to stricter postconditions. The client receives a result that meets the superclass contract, so no issues arise. is false because stricter postconditions can break clients. The client silently ignores the stricter postcondition, so behavior is unaffected. is incorrect; clients cannot ignore contract violations silently. The subclass method throws an exception due to the strengthened postcondition. is not guaranteed; exceptions are not implied by postcondition strengthening.
Final Answer:
Option B -> Option B
Quick Check:
Strengthening postconditions risks breaking client expectations.

Quick Trick: Strengthening postconditions breaks client assumptions and causes failures.

Common Mistakes:

MISTAKES

Assuming stricter postconditions are safe
Believing clients ignore contract violations
Confusing exceptions with contract violations

Trap Explanation:

PITFALL

Options A and C reflect common misconceptions that stricter guarantees are harmless or ignored; option D confuses contract violation with runtime exceptions.

Interviewer Note:

CONTEXT

Tests understanding of behavioral contracts and consequences of violating postconditions.

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Solution Trace

More OOP & Design Patterns Quizzes

Trace the sequence of events when a client calls a method on a subclass instance that violates the Liskov Substitution Principle by strengthening a postcondition. What happens step-by-step?

Step 1: Recall LSP postcondition rule

Step 2: Trace client call

Step 3: Analyze options

Final Answer:

Quick Check:

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