Adapter
- Convert the interface of a class into another interface clients expect.
- Adapter lets classes work together that couldn't otherwise because of
incompatible interfaces.

- Target : Defines the domain-specific interface that Client uses.
- Client : Collaborates with objects conforming to the Target
interface.
- Adaptee : Defines an existing interface that needs adapting.
- Adapter : Adapts the interface of Adaptee to the Target interface.
- you want to use an existing class, and its interface does not match the
one you need.
- you want to create a reusable class that cooperates with unrelated or
unforeseen classes, that is, classes that don't necessarily have compatible
interfaces.
- (object adapter only) you need to use several existing subclasses, but
it's impractical to adapt their interface by subclassing every one. An
object adapter can adapt the interface of its parent class.
- Class and object adapters have different trade-offs.
- A class adapter
- adapts Adaptee to Target by committing to a concrete Adapter class. As
a consequence, a class adapter won't work when we want to adapt a class
and all its subclasses.
- lets Adapter override some of Adaptee's behavior, since Adapter is a
subclass of Adaptee.
- introduces only one object, and no additional pointer indirection is
needed to get to the adaptee.
- An object adapter
- lets a single Adapter work with many Adaptees—that is, the Adaptee
itself and all of its subclasses (if any). The Adapter can also add
functionality to all Adaptees at once.
- makes it harder to override Adaptee behavior. It will require
subclassing Adaptee and making Adapter refer to the subclass rather than
the Adaptee itself.