Applying the Interface pattern, the common services offered by different service provider classes can be abstracted out and declared as a separate interface. Each of the service provider classes can be designed as implementers of this common interface.
With this arrangement, the client can safely assume the service provider object to be of the interface type.objects of different service provider classes can be treated as objects of the interface type. This enables the client to use different types of service provider objects in a seamless manner without requiring any changes. The client does not need to be altered even when a new service provider is introduced.
Prototype
Example
Let us build an application to calculate and display the salaries of dif ferent
employees of an organization with the categorization of designations as listed in
| Designations | Category |
|---|---|
| Programmer, Designer and Consultant | Category-A |
| Sales Rep, Sales Manager, Account Rep | Category-B |
| … | … |
| C-Level Executives | Category-n |
| … | … |
Poor design
Let us assume that the application needs to consider only those employees whose designations are part of Category-A. And we design the application only for the Category-A. But when later found the Category-B. Then we have to Alter the emplyee class and make it compatible with the Category-B also. So this a result of bad poor design.
Correct Design
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