Recap: Adapter Pattern

Adapter lets a client use an existing class whose interface does not fit, by putting a translating class between them.

• Intent. Convert the interface of a class into another interface clients expect, so incompatible classes can work together.
• Participants. The target is the client's interface, the adaptee is the existing class, and the adapter implements the target and calls the adaptee.
• Object or class adapter. The object adapter holds the adaptee and is the usual form; the class adapter inherits from it.
• Recognise it by shape. A class that implements one interface and forwards each call, translated, to an object with another.
• In the wild. InputStreamReader is a Reader made from an InputStream; Arrays.asList is a List over an array, which cannot grow.
• The trap. An adapter only translates. A rule that would still be needed without the mismatch belongs outside it.