Adapter Design Pattern
Also Known as Wrapper
why use it ?
This type of design pattern lets any user to convert one interface to another. This lets classes work together which could not be done earlier due to incompatible interface.
problems Faced :
There is an interface named ToolKit which has some common method for the editor,like view() for showing a shape defined in TextView class, delete() to delete a shape.
Suppose there is a drawing editor.In that line,rectangle,triangle can be drawn by some graphical
object which has two methods for editing named edit() and drawing named draw().The interface named
CommonShape for this graphical object is defined in a abstract class called Shape .To draw a line LineShape class is defined which is a subclass of Shape,similarly to draw a triangle TriangleShape class of subclass Shape is defined.
Now we want to implement an other features for TextShape which requires two methods for
showing and edit the text.Now,for edit the text edit() is defined in Shape class and can be reused,But there is no method for view() the text.
So, to implements the TextShape we have to use TextView for showing the text and CommonShape foredit and write the text.But we can’t use these together.we can’t also reuse the logic of view() in Shape class but the logic is not visible in ToolKit as it is an interface.
May be A Solution
1. By using an composition.view() method can be redefined in Different LineShape,TextShape class according to the requirement.
2. By implementing the main interface as per requirements.
Where we can apply this?
1. Reusing an existing class,whose interfaces are not same. class adaptor(__using inheritance__)
2. When we need to inherit one class to other.Then there may be some common methods and other methods too.So we can’t define all methods in one interface only.So there we can also use this pattern. object adaptor(__using composition__)
Design :
1. Target Interface : desired interface class, which will be directly used by the user.
2. adapter class : A wrapper class Which implements the actual logic for user.It is also used to modify the existing adpatee class method’s logic.
3. adaptee class : It implements the actual interface and defines the logic.This class is used in adapter class.
4. clients : it implements the UI view for whole application which will interact with adapter class.
Advantages :
- It increases the “Reusability” of the code and decreases the “Duplicity”.
Types :
1. Class Adaptor : Mainly design by implements the interface directly. And an abstract class is used as a adptee class.An adapter class is used to modofy the existing logic in apatee class.
2. Object Adaptor : Here we used composition instead of inheritance , rest are same as class adpater.
UML Diagram
