Wrapper pattern

In software engineering, the adapter pattern is a software design pattern (also known as Wrapper, an alternative naming shared with the Decorator pattern) that allows the interface of an existing class to be used as another interface. It is often used to make existing classes work with others without modifying their source code.

An example is an adapter that converts the interface of a Document Object Model of an XML document into a tree structure that can be displayed.

An adapter allows two incompatible interfaces to work together. This is the real world definition for an adapter. Interfaces may be incompatible, but the inner functionality should suit the need. The Adapter design pattern allows otherwise incompatible classes to work together by converting the interface of one class into an interface expected by the clients.

An adapter can be used when the wrapper must respect a particular interface and must support polymorphic behavior. Alternatively, a decorator makes it possible to add or alter behavior of an interface at run-time, and a Facade is used when an easier or simpler interface to an underlying object is desired.

There are two adapter patterns:

In this adapter pattern, the adapter contains an instance of the class it wraps. In this situation, the adapter makes calls to the instance of the wrapped object.

This adapter pattern uses multiple polymorphic interfaces implementing or inheriting both the interface that is expected and the interface that is pre-existing. It is typical for the expected interface to be created as a pure interface class, especially in languages such as Java (before jdk 1.8) that do not support multiple inheritance of classes.

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