# Facade Pattern ## What? * a facade encapsulates a complex subsystem behind a simple interface. It hides much of the complexity and makes the subsystem easy to use. * Used for complex complex systems of clases, libraries or frameworks * Recognised by the use of a simple interface, but under the hood (implementation) is complex * The client only interacts with the Façade class without knowing about the subsystem classes. * The subsystem that the facade abstracts over doesnot know anything (not dependent) about the facade ## Why? * Layering: Facade pattern can be used in applications for creating a layer to abstract and unify the related interfaces in the application. Use of a facade will define an entry point to each subsystem level and thus make them communicate only through their facades; this can simplify the dependencies between them. ### Benefits * It decouples a client implementation from the complex subsystem. * we can make changes to the existing subsystem and don't affect a client. * Façade makes the API and libraries easier to use which is good for maintenance and readability. * It can collate and abstract various poorly designed APIs with a single simplified API. * It reduces dependencies of the external code on the inner working of the libraries and thus providing flexibility. * increases loose coupling ### Drawbacks * Lead to lots of levels of abstraction and indirection * Can be overused for simple implementations * the subsystem methods are connected to the Façade layer. If the structure of the subsystem changes then it will require subsequent change to the Façade layer and client methods. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://hanfak.gitbook.io/workspace/general-paradigms/patterns/gangoffour/facade.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.