Adapter structural pattern

An adapter is a special object that converts the interface of one object so that another object can understand it.

It wraps one of the objects to hide the complexity of conversion happening behind the scenes.

The wrapped object isn’t even aware of the adapter.

For example, you can wrap an object that operates in meters and kilometers with an adapter that converts all of the data to imperial units such as feet and miles.

Adapters can not only convert data into various formats but can also help objects with different interfaces collaborate.

When should you use it ?

• Use the Adapter class when you want to use some existing class, but its interface isn’t compatible with the rest of your code.
• Use the pattern when you want to reuse several existing subclasses that lack some common functionality that can’t be added to the superclass.

How do you implement it ?

1. Make sure that you have at least two classes with incompatible interfaces:
• A useful service class, which you can’t change (often 3rd-party, legacy or with lots of existing dependencies).
• One or several client classes that would benefit from using the service class.
2. Declare the client interface and describe how clients communicate with the service.
3. Create the adapter class and make it follow the client interface. Leave all the methods empty for now.
4. Add a field to the adapter class to store a reference to the service object. The common practice is to initialize this field via the constructor, but sometimes it’s more convenient to pass it to the adapter when calling its methods.
5. One by one, implement all methods of the client interface in the adapter class. The adapter should delegate most of the real work to the service object, handling only the interface or data format conversion.
6. Clients should use the adapter via the client interface. This will let you change or extend the adapters without affecting the client code.