Intermediate Object-Oriented Programming test (Intermediate)

Sample questions

5 sample questions from the Intermediate Object-Oriented Programming test, with the answers. Samples are taken out of the live test, so you will not meet these when you sit it.

1. A system has a large interface with many methods, but most classes only use a few of them. How should you apply the Interface Segregation Principle to improve the design?

   1. Split the interface into smaller, role-specific interfaces so that classes only depend on the methods they need.
   2. Use inheritance to allow classes to selectively override only the methods they need.
   3. Keep the interface as is and let classes ignore the methods they don't need.
   4. Create a new abstract class that implements the interface and provides default implementations for unused methods.

   Answer: A. Split the interface into smaller, role-specific interfaces so that classes only depend on the methods they need.

   The Interface Segregation Principle (ISP) states that clients should not be forced to depend on methods they do not use. To apply this principle, you should split a large, fat interface into smaller, role-specific interfaces so that each class only depends on the methods it actually needs. This reduces coupling and improves maintainability.

2. You are designing a module that processes payments, and you need to support multiple payment processors (e.g., PayPal, Stripe). Which of the following options best demonstrates the use of a has-a relationship to model this scenario?

   1. Use composition to allow the module to dynamically switch between different payment processors without modifying its code.
   2. Use inheritance to allow the module to dynamically switch between different payment processors without modifying its code.
   3. Use an interface to define the payment processing logic that all payment processors must follow.
   4. Use an abstract class to define the payment processing logic that all payment processors must follow.

   Answer: A. Use composition to allow the module to dynamically switch between different payment processors without modifying its code.

   Composition allows a module to contain and delegate to other objects, enabling flexibility and loose coupling. This approach avoids the rigid hierarchy and tight coupling that inheritance can introduce. It also supports the Open/Closed principle by allowing new payment processors to be added without altering the module's code. The other options either describe inheritance or fail to address the benefits of composition in this context.

3. What is the purpose of a UML association role name?

   1. A UML association role name is used to describe the name of the association from the perspective of the class it belongs to, and it clarifies the nature of the relationship between the classes.
   2. A UML association role name is used to define the visibility of the association in the diagram, such as public, private, or protected.
   3. A UML association role name is used to denote the multiplicity of the association, such as 1, 0..1, or *.
   4. A UML association role name is used to describe the number of objects that can be involved in the relationship.

   Answer: A. A UML association role name is used to describe the name of the association from the perspective of the class it belongs to, and it clarifies the nature of the relationship between the classes.

   A UML association role name is used to describe the name of the association from the perspective of the class it belongs to. This is important for clarity in UML class diagrams, as it helps distinguish the roles of the classes in the relationship. The other options are incorrect because they either misrepresent the purpose or are not accurate descriptions of UML association role names.

4. Which of the following approaches best helps avoid tight coupling between classes in an object-oriented design?

   1. Inherit from a base class to reuse common functionality across multiple classes.
   2. Use static methods to access shared state and behavior between classes.
   3. Use dependency injection to decouple classes by injecting dependencies through constructors or setters.
   4. Hardcode dependencies directly within the class using the new keyword.

   Answer: C. Use dependency injection to decouple classes by injecting dependencies through constructors or setters.

   Dependency injection allows classes to depend on abstractions rather than concrete implementations, reducing coupling. This promotes flexibility and maintainability by enabling dependencies to be swapped at runtime without modifying the dependent class. Other options either increase coupling or do not directly address the issue of tight coupling.

5. Which of the following statements is true about implementing an interface in object-oriented programming?

   1. A class implementing an interface does not need to provide implementations for any methods.
   2. Interfaces in Java cannot contain abstract methods.
   3. A class implementing an interface must provide concrete implementations for all abstract methods in that interface.
   4. A class can selectively implement only some of the abstract methods in an interface.

   Answer: C. A class implementing an interface must provide concrete implementations for all abstract methods in that interface.

   In object-oriented programming, when a class implements an interface, it must provide concrete implementations for all abstract methods defined in the interface. This ensures that the class adheres to the contract defined by the interface, allowing for polymorphism and consistent behavior across different implementations. The other options are incorrect because they either describe inheritance, provide misleading information, or are not universally true in all programming languages.