Skill Development Lab (AL-705) - Important Questions

Explain the concept of Design Patterns and their role in software engineering. Classify design patterns into Creational, Structural, and Behavioral categories and give two representative examples with brief use-cases for each category.

Implement and explain the Factory Method pattern for a class hierarchy of shapes (Circle, Rectangle, Square). Provide the class diagram and code snippets, and explain the difference between Factory Method and Abstract Factory with an example scenario for each.

Implement and explain the Observer pattern for a publisher-subscriber scenario (for example, a News Agency notifying Subscribers). Provide class and sequence diagrams, sample code, and discuss concurrency/thread-safety considerations and typical applications.

Compare Adapter, Facade, and Proxy design patterns. For each pattern give a clear example, draw the UML class diagram, and state typical scenarios where you would prefer one over the others.

Explain the Singleton pattern and implement a thread-safe Singleton in a programming language of your choice. Discuss drawbacks, testing difficulties, and alternative approaches to achieve similar goals.

Describe the Strategy and State design patterns. Provide an example where Strategy is more appropriate than State and an example where State is the better choice. Include class diagrams and a short implementation of one example.

Explain the Decorator pattern and contrast it with using inheritance to extend behavior. Provide a UML diagram and code snippet demonstrating how Decorator adds responsibilities at runtime, and discuss performance or complexity impacts.

Explain the Command pattern and implement a simple Undo/Redo mechanism for editor operations (e.g., InsertText, DeleteText). Provide class and sequence diagrams, sample code for command execution and undo, and discuss how to persist or serialize command history if required.

What are the SOLID principles? For each principle, explain it briefly and give at least one design pattern that helps to realize or support that principle in system design.

Discuss the Model-View-Controller (MVC) architecture as an application of design patterns. Identify common design patterns used within MVC implementations (for example, Observer, Strategy) and justify their usage with examples.

Given a case study where a system must allow adding responsibilities to objects dynamically and support combining multiple features at runtime, choose the appropriate design pattern(s), justify your choice, and outline a possible implementation (include class diagram and brief pseudo-code).

List common anti-patterns and pitfalls in using design patterns. Provide examples of overuse or misuse of patterns such as Singleton and Factory, and describe how such misuse can be identified and corrected.