CPSA Software Design Principles 4 — Questions and Answers
Question 1: Interface Segregation Principle (ISP) recommends that clients should NOT be forced to depend on interfaces they do not use. What is the PRIMARY design remedy?
- Merge all interfaces into one comprehensive interface
- Split large interfaces into smaller, role-specific ones (Correct answer)
- Replace interfaces with abstract classes
- Use adapter patterns to wrap the large interface
Correct answer: Split large interfaces into smaller, role-specific ones
ISP recommends splitting fat interfaces into multiple focused, role-specific interfaces so clients only depend on the methods they actually use.
Question 2: Which term describes the degree to which elements within a module belong together and relate to a single purpose?
- Coupling
- Cohesion (Correct answer)
- Encapsulation
- Abstraction
Correct answer: Cohesion
Cohesion measures how closely related and focused the responsibilities of a single module are — high cohesion means all elements serve a common purpose.
Question 3: Preferring composition over inheritance is recommended primarily because composition:
- Eliminates the need for interfaces entirely
- Avoids breaking changes when parent class internals change (Correct answer)
- Always produces faster runtime performance
- Requires less code than inheritance hierarchies
Correct answer: Avoids breaking changes when parent class internals change
Composition avoids the fragile base class problem — changes to a parent class cannot break subclasses because composed objects are accessed through interfaces, not inherited directly.
Question 4: What quality attribute is MOST directly improved by applying abstraction in software design?
- Security
- Modifiability / maintainability (Correct answer)
- Throughput
- Fault tolerance
Correct answer: Modifiability / maintainability
Abstraction hides implementation details behind stable interfaces, making it easier to change internals without affecting dependent components, directly improving modifiability.
Question 5: Which scenario is an example of 'feature envy' as a code smell related to design principles?
- A class with too many public methods
- A method that uses data and methods from another class more than its own (Correct answer)
- A subclass overriding all parent methods
- An interface with a single method
Correct answer: A method that uses data and methods from another class more than its own
Feature envy occurs when a method accesses another object's data far more than its own class's data, suggesting the method may belong in the other class.
Question 6: In the CPSA (iSAQB) framework, which concept describes the degree to which software components can be understood, changed, and tested in isolation?
- Availability
- Modifiability (Correct answer)
- Interoperability
- Scalability
Correct answer: Modifiability
Modifiability (maintainability) refers to how easily software can be understood, modified, extended, and tested, which is a primary goal of good design principles.
Question 7: Which of the following BEST illustrates a violation of the Dependency Inversion Principle?
- A high-level business logic class directly instantiates a specific database class (Correct answer)
- A class implements two different interfaces
- A method returns an interface type rather than a concrete type
- A module depends on an abstract factory
Correct answer: A high-level business logic class directly instantiates a specific database class
When a high-level module directly instantiates a concrete low-level class (e.g., a specific database), it creates a hard dependency on implementation details, violating DIP.
CPSA Software Design Principles 4
Interface Segregation Principle (ISP) recommends that clients should NOT be forced to depend on interfaces they do not use.
What is the PRIMARY design remedy?