Adapter

and one making use of delegation:

Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. (See the STL container adaptors for a good example of adapting template containers.)

Applicability

• Need to using an existing class, but its interface doesn't match
• Need to make use of incompatible classes
• (object adapter) Need to use several existing subclasses, but don't what to subclass them all

Consequences

• Class adapter commits to the concrete Adapter class: it won't work with Adapter's subclasses, but object adapter does.
• Class adapter introduces only one object and no ponter indirection
• Object adapter requires quite a bit of work, since all of Adaptee's interface must be duplicated.