Adapter

Adapter Concept

The Adapter pattern (a.k.a Wrapper, similar to the Decorator pattern) is a structural design pattern commonly used to wrap a pre-existing class. It allows a class to work with others without altering the core, by encapsulating it with an additional layer.

In practical software development, situations often arise where there is a need to integrate external libraries (DLL). The challenge is to incorporate additional functionality without affecting the core.

Consider a scenario where an existing system already has functionality for controlling a light source with methods for turning it On/Off.

Now, the goal is to integrate a new controller into the system. The new controller also has methods for turning on & off, but even if the method has same names, they cannot be directly used due to the absence of a shared interface.

Adapter Example

//*************
//* author: cian
//* 20231017
//**************

/* Adapter Interface */
interface ILightControl
{
    void Open();
    void Close();
}

class SomeLightControllerAdapter : ILightControl
{
    private SomeLightController adaptee = new SomeLightController();

    public void Open()
    {
        adaptee.LightOpen(); //method wrapped.
    }

    public void Close()
    {
        adaptee.LightClose(); //method wrapped.
    }
}

class MainApp
{
    static void Main(string[] args)
    {
        var lightList = new List<ILightControl>();
        lightList.add(new OriginLightController());
        lightList.add(new SomeLightControllerAdapter());
        
        foreach (var item in lightList)
        {
            item.Open();
        }
    }
}

Personally, I think Adapter pattern is a common application of interfaces, especially for those who have experience working with external APIs. It’s easy to grasp the concept if you’ve experienced in system integration.

References

• DESIGN PATTERNS: ELEMENTS OF REUSABLE OBJECT-ORIENTED SOFTWARE