No client should be forced to depend on a method it does not use
Consider example of office space where various output devices are represented using objects
Before Interface Segregation Principle:
IMultiFunction Interface
/**
* @ImultiFunction interface has methods related to all output devices present in office space
* for devices like Printer, Scanner, Fax machines, etc
*/
public interface IMultiFunction {
public void print();
public void getPrintSpoolDetails();
public void scan();
public void scanPhoto();
public void fax();
public void internetFax();
}
Now implementing the above common interface for various devices
XeroxWorkCenter class having all capabilities
/**
*
* You must have seen Xerox work station device which has all the features in one like printing, scanning, xerox,
* fax etc
*/
public class XeroxWorkCenter implements IMultiFunction {
@Override
public void print() {
// real printing code
}
@Override
public void getPrintSpoolDetails() {
// real get print spool details code
}
@Override
public void scan() {
// read scanning code
}
@Override
public void scanPhoto() {
// real scan photo code
}
@Override
public void fax() {
// real fax code
}
@Override
public void internetFax() {
// real internet fax code
}
}
HpPrinterNScanner class has printing and scanning capabilities
public class HpPrinterNScanner implements IMultiFunction {
@Override
public void print() {
// real printing code
}
@Override
public void getPrintSpoolDetails() {
// real get print spool details code
}
@Override
public void scan() {
// read scanning code
}
@Override
public void scanPhoto() {
// real scan photo code
}
//Since HpPrinterNScanner has only printing and scanning abilities fax() and internetFax() will have empty body
@Override
public void fax() {}
@Override
public void internetFax() {}
}
CanonPrinter class has only printing capability
public class CanonPrinter implements IMultiFunction {
@Override
public void print() {
// real printing code
}
@Override
public void getPrintSpoolDetails() {
// real get print spool details code
}
//Since the CanonPrinter has only printing ability rest of the method will have an empty body
@Override
public void scan() {}
@Override
public void scanPhoto() {}
@Override
public void fax() {}
@Override
public void internetFax() {}
}
Techniques to identify the violation of ISP
- Fat interfaces (Interfaces having two many method declarations)
- Interfaces with low cohesion (interfaces having methods that are not likely to be related to each other)
- *Empty methods implementation *( when classes are forced to implement methods that they don't use, they leave the implementation of the methods with blank body)
After Interface segregation principle:
public interface IPrint {
public void print();
public void getPrintSpoolDetails();
}
public interface IScan {
public void scan();
public void scanPhoto();
}
public interface IFax {
public void fax();
public void internetFax();
}
/**
*
* You must have seen the Xerox workstation device which has all the features in one like printing, scanning, xerox, fax, etc.
*/
public class XeroxWorkCenter implements IPrint,IScan,IFax {
@Override
public void print() {
// real printing code
}
@Override
public void getPrintSpoolDetails() {
// real get print spool details code
}
@Override
public void scan() {
// read scanning code
}
@Override
public void scanPhoto() {
// real scan photo code ̰
}
@Override
public void fax() {
// real fax code
}
@Override
public void internetFax() {
// real internet fax code
}
}
public class HpPrinterNScanner implements IPrint,IScan {
@Override
public void print() {
// real printing code
}
@Override
public void getPrintSpoolDetails() {
// real get print spool details code
}
@Override
public void scan() {
// read scanning code
}
@Override
public void scanPhoto() {
// real scan photo code
}
}
public class CanonPrinter implements IPrint {
@Override
public void print() {
// real printing code
}
@Override
public void getPrintSpoolDetails() {
// real get print spool details code
}
}
Each Interface has a single responsibility and is much cleaner now.
Relation that ISP holds with other SOLID principles
Single responsibility
After the segregation of the interfaces into different interfaces, now all the interfaces like IPrint, IScan have a single responsibility
Liskov substitution
Due to the segregation now all the classes (implementing the interfaces) follow Liskov substitution, as all the subtypes or implementing classes can be replaced with their interface reference variable
Top comments (0)