CPSA Software Design Principles Questions and Answers

Question 1

A software architect is designing a system where a `ReportGenerator` class needs access to customer data.
Instead of allowing `ReportGenerator` to directly instantiate a `CustomerRepository` class, the architect mandates that `ReportGenerator` must depend on an `ICustomerRepository` interface.
The concrete implementation will be provided at runtime.
Which SOLID principle is primarily being applied?

Accepted Answer

Dependency Inversion Principle

Answer

Single Responsibility Principle

Answer

Open/Closed Principle

Answer

Liskov Substitution Principle

Question 2

A team is developing a `PaymentProcessor` class that initially only handles credit card payments. A new requirement emerges to also support payments via a third-party gateway like PayPal. To adhere to the Open/Closed Principle, what is the BEST course of action?

Accepted Answer

Refactor the `PaymentProcessor` to use a strategy pattern, where different payment methods are implemented as separate classes that conform to a common `IPaymentStrategy` interface.

Answer

Modify the `PaymentProcessor` class with an if-else statement to check the payment type and call the appropriate logic.

Answer

Create a `PayPalProcessor` class and have the client code decide which processor class to instantiate.

Answer

Add a new `processPayPalPayment` method directly to the existing `PaymentProcessor` class.

Question 3

You are reviewing a class called `UserManager` that performs the following tasks: authenticates user credentials against a database, sends a welcome email to new users, formats user data into a JSON string for an API response, and logs every login attempt to a file. This class most clearly violates which design principle?

Accepted Answer

Single Responsibility Principle

Answer

Interface Segregation Principle

Answer

Low Coupling

Answer

Information Expert

Question 4

A system has a base class `Bird` with a method `fly()`. A new requirement calls for adding an `Ostrich` class. Since an ostrich is a bird, the new class inherits from `Bird`. However, ostriches cannot fly, so the developer overrides the `fly()` method to throw a `NotSupportedException`. Why is this a violation of the Liskov Substitution Principle (LSP)?

Accepted Answer

Because an `Ostrich` object cannot be used wherever a `Bird` object is expected without potentially breaking the program's correctness.

Answer

Because the `Ostrich` class adds new methods not present in the `Bird` class.

Answer

Because the `fly()` method in the subclass has a different performance profile than the base class method.

Answer

Because inheritance should not be used for 'is-a' relationships; composition is always preferred.

Question 5

An architect is designing a modular system. They notice that a change to the `User` module frequently necessitates changes in the `Order`, `Invoice`, and `Shipping` modules. This is a symptom of what undesirable characteristic?

Accepted Answer

High Coupling

Answer

Low Cohesion

Answer

High Cohesion

Answer

Low Coupling

Question 6

A developer creates a large, general-purpose interface called `IWorker` with methods for `work()`, `eat()`, and `sleep()`. They then create a `Robot` class that implements `IWorker`. The `Robot` can `work()`, but the `eat()` and `sleep()` methods are irrelevant and are implemented by throwing an exception or doing nothing. Which SOLID principle is being violated?

Accepted Answer

Interface Segregation Principle

Answer

Open/Closed Principle

Answer

Liskov Substitution Principle

Answer

Single Responsibility Principle