design-patterns

| Complex object construction | Builder | | Create objects without specifying class | Factory | | Multiple algorithms, swap at runtime | Strategy | | Add behavior without changing class | Decorator | | Notify multiple objects of changes | Observer | | Ensure single instance | Singleton | | Convert incompatible interfaces | Adapter |

Use when: Need to create objects without specifying exact class.

Use when: Multiple algorithms for same operation, need to swap at runtime.

常见设计模式与 Java 示例（工厂、构建器、策略、观察者、装饰器等）。当用户询问“实现模式”、“使用工厂”、“策略模式”或设计可扩展组件时使用。 来源：decebals/claude-code-java。