Interfacer Segregation Principle

Interfacer Segregation Principle
Encapsulates components to increase their flexibility, testability, stability and changeability. Internal data structures are hidden, while functionality is available via defined interfaces. This principle has been defined by David L. Parnas in 1972.

Example
The example code is based on Spring MVC.
\r\n

package com.fas.cdbprovider.Controller.Service;
import com.fas.cdbprovider.Controller.Dao.CdbDao;
import com.fas.cdbprovider.Controller.Entity.Cdb;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
import java.util.Collection;

@Service
public class CdbService {
    @Autowired
    @Qualifier("fakeData")
    private CdbDao cdbDao;
    // …
}

As illustrated above, access to cdbDao is provided through encapsulation. The concrete implementation of the required object is referenced via the annotation @Qualifier. Developer references the interface of cdbDao only which encapsulates the concprete implementation FakeCdbDaoImpl class.