Advanced Object-Oriented Programming test (Advanced)

Sample questions

5 sample questions from the Advanced 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. Which of the following accurately describes the difference between the Proxy and Adapter patterns in terms of their intended use?

   1. The Proxy pattern is used to encapsulate a group of related objects, while the Adapter pattern is used for dynamic access control.
   2. The Proxy pattern is preferred when access control logic needs to be implemented dynamically at runtime, while the Adapter pattern is used when the interface of an existing class needs to be converted to a different interface expected by the client.
   3. The Proxy pattern is preferred when the interface of an existing class needs to be converted to a different interface expected by the client, while the Adapter pattern is used for dynamic access control.
   4. The Proxy pattern is used for dynamic access control, while the Adapter pattern is used to encapsulate a group of related objects.

   Answer: B. The Proxy pattern is preferred when access control logic needs to be implemented dynamically at runtime, while the Adapter pattern is used when the interface of an existing class needs to be converted to a different interface expected by the client.

   The Proxy pattern is designed to control access to an object, such as implementing lazy loading, remote access, or protection logic. It provides a wrapper that manages access control dynamically. In contrast, the Adapter pattern is used to adapt the interface of one class to another, making them compatible without changing their core functionality. The Proxy pattern is the correct choice for implementing access control logic, whereas the Adapter pattern is for interface conversion.

2. When implementing the Prototype pattern, what should you do if the object contains nested or complex structures?

   1. Use the Prototype pattern only when the object is immutable.
   2. Use a shallow copy to save memory and optimize performance.
   3. Use a deep copy to ensure the cloned object has its own separate state, avoiding unintended side effects.
   4. Avoid cloning and instead use a factory method to create new objects.

   Answer: C. Use a deep copy to ensure the cloned object has its own separate state, avoiding unintended side effects.

   The Prototype pattern relies on cloning an existing object. When using the Prototype pattern, a common mistake is not considering whether a shallow or deep copy is needed. In cases where the object contains nested or complex structures, a shallow copy could lead to unintended side effects because changes to the cloned object might affect the original. Therefore, using a deep copy is the correct approach to ensure that the cloned object has its own independent state.

3. Which GoF design pattern is best suited for encapsulating interchangeable algorithms that can be chosen at runtime based on the context, allowing the same interface to be used with different implementations?

   1. Strategy
   2. Observer
   3. Adapter
   4. Decorator

   Answer: A. Strategy

   The Strategy pattern is used to encapsulate interchangeable algorithms behind one interface, allowing them to be chosen at runtime. This matches the scenario where different algorithms are applied to the same data, and the choice of algorithm is determined dynamically. Other patterns like Adapter, Decorator, and Observer do not fit this intent.

4. Which of the following best describes how the Adapter pattern works internally?

   1. Adapter pattern changes the interface of an existing class to match the expected interface of a client, without modifying the existing class's code.
   2. Adapter pattern adds new functionalities to an object at runtime by wrapping it with another object that implements the same interface.
   3. Adapter pattern controls access to an object by wrapping it with a proxy that enforces access rules.
   4. Adapter pattern creates a family of related objects that are used together, ensuring that they are compatible with each other.

   Answer: A. Adapter pattern changes the interface of an existing class to match the expected interface of a client, without modifying the existing class's code.

   The Adapter pattern is used to make incompatible interfaces work together by converting the interface of one class into another that the client expects. It does not change the existing class's code but instead wraps it in a new class that provides the required interface. This allows the client to interact with the existing class as if it had the desired interface, without modifying the original class.

5. Which statement is correct regarding the refactoring of sealed abstract methods in object-oriented programming?

   1. Refactoring sealed abstract methods is not possible due to performance overhead, as sealed classes require additional runtime checks.
   2. Refactoring sealed abstract methods is only possible if the abstract method is marked as final, preventing any subclass modifications.
   3. Refactoring sealed abstract methods is not possible because sealed classes cannot be extended outside their defining module, limiting the ability to introduce new subclasses during refactoring.
   4. Refactoring sealed abstract methods is possible by using inheritance in other modules, as the sealed modifier does not restrict inheritance globally.

   Answer: C. Refactoring sealed abstract methods is not possible because sealed classes cannot be extended outside their defining module, limiting the ability to introduce new subclasses during refactoring.

   Sealed classes are designed to restrict inheritance to a known set of subclasses within the same module. This restriction makes it impossible to refactor sealed abstract methods by introducing new subclasses outside the module, as the sealed modifier enforces this limitation. The other options are incorrect because they either describe unrelated concepts or inaccurately represent the behavior of sealed classes.