CodeParkThey differ in their goal and in the interface they show to the caller.
Adapter converts one interface into another interface that the client expects. Example: StripePaymentGateway implements your PaymentGateway interface. It translates each call into a call to the Stripe SDK.
Facade gives one simpler interface over a whole subsystem. Example: CheckoutFacade.placeOrder() hides the calls to inventory, pricing, payment and email.
Decorator keeps the same interface and adds behaviour. You can stack decorators inside each other: new RetryingNotifier(new LoggingNotifier(email)).
Proxy also keeps the same interface. But its job is to control access to the real object. It can be used for:
- lazy creation (create the real object only when first needed)
- caching
- access checks
- standing in for a remote object
In short:
- Adapter changes the interface.
- Facade turns many interfaces into one simple one.
- Decorator adds features and keeps the same interface.
- Proxy controls access and keeps the same interface.
- Adapter translates an existing interface into the one the client needs.
- Facade is one simple entry point over a subsystem.
- Decorator keeps the same interface, adds behaviour, and can be stacked.
- Proxy keeps the same interface and controls access, for lazy creation, caching, auth or remote objects.
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