As a project evolves, you find you have different problems to solve. Many of these problems require re-engineering, while others can be solved by reusing some existing code or object.

Here is the scenario, your application has a predefined interface say IPrintable which has the single method Print(). Your internal objects all already inherit from the IPrintable interface, so they all have their respective Print() method defined.

A few weeks into the project, you find you can use an off the shelf component ComponentA to handle a certain functionality. However, all your objects need to be part of IPrintable and this off the shelf component doesn't have it and additionally you cannot modify it since you do not have the source code for the object.

Now What? Here, a simple application of the Adaptor pattern can save the day. You have probably already written an object based on the adaptor pattern in the past without even knowing it!

To apply the adaptor pattern, as the name implies, you create your own class MyClass inheriting from ComponentA and you also inherit the IPrintable interface used within your project. You can now use MyClass as an IPrintable object anywhere in your project, and you can also define the Print() to include information from ComponentA .

Note: Sometimes it is impossible to apply inheritance for components, however in such a scenario you can simply make ComponentA a private instance of MyClass.