CSC/ECE 517 Fall 2009/wiki3 8 ISPPSI

Interface Segregation Principle vs. Principle of Small Interfaces

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Introduction

This page tries to review Integrated Development Environments for Ruby such as Aptana,Rubymine and Netbeans. Also the IDEs are compared with respect to certain dimensions such as facilities, ease of use, system requirements, and support for the Ruby way of thinking.

Interface Segregation Principle

• “Many client specific interfaces are better than one general purpose interface“
• “The dependency of one class to another one should depend on the smallest possible interface“
• “Make fine grained interfaces that are client specific.“
• “Clients should not be forced to depend upon interfaces that they don’t use. This principle deals with the disadvantages of fat interfaces. Fat interfaces are not cohesive. In other words the interfaces of classes should be broken into groups of member functions.“

Here is an example of a real system where the Interface-Segregation Principle is required to make the client usage simple.

Consider a User interface for ATM machine with a UI that allows conducting a

1) Deposit Transaction,

2) Withdrawal Transaction, and

3) Transfer Transaction.

The end goal is to have a seamless user experience for a user with a fast turnaround time. You would definitely separate these 3 interfaces from each other so that one type of transaction does not depend on functions it does not need and in turn cause confusion to the final client.

When clients are forced to depend upon interfaces that they don’t use, then those clients are subject to changes to those interfaces. This results in an inadvertent coupling between all the clients. Said another way, when a client depends upon a class that contains interfaces that the client does not use, but that other clients do use, then that client will be affected by the changes that those other clients force upon the class. We would like to avoid such couplings where possible, and so we want to separate the interfaces where possible.

Clients Should not be forced to use Interface they don't use

To explain this consider the following Java Code

Consider an Interface shown below

interface Iworker{
       public void work();
       public void eat();
                  }

If we try to implement a class worker using above interface, the worker is allocated some time for working during which work() is used and during lunch break eat() is used. But if we try to implement a robot, then we are forced to use eat() on robot also though it is not using it. We are forcing robot to use eat() which is not being used.

So we have to use different type of interface which doesn't force interfaces on clients which are not used. The following code explains it.

interface IWorker extends Feedable, Workable {
}
interface IWorkable {
	public void work();
}

interface IFeedable{
	public void eat();
}

class Worker implements IWorkable, IFeedable{
	public void work() {
		// ....working
	}

	public void eat() {
		//.... eating in launch break
	}
}

class Robot implements IWorkable{
	public void work() {
		// ....working
	}
}

class SuperWorker implements IWorkable, IFeedable{
	public void work() {
		//.... working much more
	}

	public void eat() {
		//.... eating in launch break
	}
 }

class Manager {
	Workable worker;

	public void setWorker(Workable w) {
		worker=w;
	}

	public void manage() {
		worker.work();
	}
}

Comparision of Aptana,Netbeans and Rubymine

Three IDEs namely Aptana's Radrails, Netbeans and Rubymine are compared in the following sections.

References

http://www.oodesign.com/interface-segregation-principle.html

http://www.objectmentor.com/resources/articles/isp.pdf

http://davidhayden.com/blog/dave/archive/2005/06/15/1482.aspx