What is a design pattern, and when should you apply one?

• A. A universal solution for all problems; always apply.
• B. A code style guideline with no impact on structure.
• C. A proven solution to a recurring problem; apply when it clarifies structure or reduces complexity without overengineering.
• D. A debugging trick that bypasses design considerations.

Answer: (C)

A design pattern is a proven solution to a recurring problem in software design. It offers a way to structure code and interactions between objects that has been shown to work well in many similar situations. You apply a pattern when you face a problem that tends to recur and using the pattern clarifies the structure or reduces complexity without adding unnecessary overhead or overengineering. Patterns help communicate intent within a team and can improve maintainability and flexibility by providing established roles and interactions, not by forcing a one-size-fits-all fix. They are about design decisions and architecture, not just coding style or quick debugging tricks, and they should be chosen and adapted with judgment to balance benefits against added abstraction.