This question evaluates proficiency in classical design patterns (Singleton, Factory Method, Strategy), concurrent programming and thread safety in Java, dependency injection and refactoring to reduce coupling within the System Design domain, emphasizing practical implementation alongside conceptual architectural reasoning.

You are designing a small Java library and want to demonstrate three classic GoF design patterns with concise examples. You should:
Keep code snippets small and focused on illustrating the pattern rather than full application logic.
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