Extension Object Pattern

Extension Object is a less common but useful structural pattern for capability-based extension. Instead of putting every optional feature on the main class, the object can expose or discover extension objects that provide extra behavior.

In Java, this can help when:

• not every instance supports every capability
• optional capabilities should be added without deep hierarchy growth
• a plugin-like extension model is needed

It is more specialized than Decorator and usually more niche.

In this section

• Implementing Extension Object in Java
  Implement Extension Object in Java by exposing optional capabilities through explicit extension lookup rather than bloating the primary type.
• Adding Functionality at Runtime with the Extension Object Pattern
  Add runtime capabilities in Java carefully so extension objects stay explicit and do not turn into hidden service locator behavior.
• Extension Objects vs. Decorators
  Compare Extension Object and Decorator in Java so optional capabilities and wrapper-based behavior layering are not confused.
• Extension Object Pattern Use Cases and Examples in Java
  See where Extension Object fits in Java systems, especially plugin models, optional capabilities, and modular feature attachments.