How does Builder differ from Chain of Responsibility?

Builder and Chain of Responsibility are two completely different patterns, even though both use a step-by-step or sequential approach. The difference is in the goal and the nature of the interaction between objects.

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#1. Goal

• Builder - controls the creation of a complex object from separate parts. It assembles the product step by step until a finished instance is produced.
• Chain of Responsibility - controls handling a request: it passes it along a chain of objects until one of them handles it.

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#2. Type of interaction

• In Builder, all steps run in a defined sequence, often under the control of a "director." Each step adds a part of the future object.
• In Chain of Responsibility, objects form a chain; each one can handle the request or pass it on. Here the interaction is dynamic and conditional, not a linear construction of a result.

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#3. Context of use

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#4. Example

Builder: Assembles a Car: engine -> wheels -> interior -> build().

Chain of Responsibility: Handles a user request: logger -> authorization -> validation -> controller, until someone completes the chain.

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#5. Conclusion

• Builder is about construction (creating a product).
• Chain of Responsibility is about delegation (passing a request on).

Builder answers the question "How to build it step by step?", Chain of Responsibility answers "Who will handle it?".