Use cases

The Adapter pattern is used for making things work after they have been implemented [j.mp/adapterpat]. Usually one of the two incompatible interfaces is either foreign or old/legacy. If the interface is foreign, it means that we have no access to the source code. If it is old it is usually impractical to refactor it. We can take it even further and argue that altering the implementation of a legacy component to meet our needs is not only impractical, but it also violates the open/close principle [j.mp/adaptsimp]. The open/close principle is one of the fundamental principles of Object-Oriented design (the O of SOLID). It states that a software entity should be open for extension, but closed for modification. That basically means that we should be able to extend the behavior of an entity without making source code modifications. Adapter respects the open/closed principle [j.mp/openclosedp].

Therefore, using an Adapter for making things work after they have been implemented is a...