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Single Responsibility Principle

Single Responsibility Principle

What are S.O.L.I.D Principles?

Simply , S.O.L.I.D principles are five object oriented principles by Robert.C Martin that should be followed when designing a software.

S → Single Responsibility
O → Open Close Principle
L →  Liskov Substitution
I →   Interface Segregation
D → Dependency Inversion

Why developers should know about these principles?

The broad goal of the SOLID principles is to reduce dependencies so that engineers change one area of software without impacting others. Additionally, they’re intended to make designs easier to understand, maintain, and extend. Ultimately, using these design principles makes it easier for software engineers to avoid issues and to build adaptive, effective, and agile software.

(https://www.bmc.com/blogs/solid-design-principles/#:~:text=The%20SOLID%20principles%20were%20developed%20to%20combat%20these%20problematic%20design,understand%2C%20maintain%2C%20and%20extend)

What is the usage of solid principles?

SOLID Principles is a coding standard that all developers should have a clear concept for developing software properly to avoid a bad design. It was promoted by Robert C Martin and is used across the object-oriented design spectrum. When applied properly it makes your code more extendable, logical, and easier to read.

(https://medium.com/mindorks/solid-principles-explained-with-examples-79d1ce114ace)

Single Responsibility

Here in this blog , i am going to discover about Single Responsibility Principle through in this four sections


1) Introduction
2) Usage 
3) Violations of Single Responsibility
4) Benefits

1) Introduction

"A class should have one and only one reason to change, meaning that a class should have only one job"

This is the statement that we can found in anywhere when you search it in google.

When we takes a computer program , it may contains many classes. So each class of the computer program must have responsibility over a single part of that program’s functionality,which should encapsulates.(Wikipedia)

That means, there may not contain classes that are not having any duty with the program. Every class in the program must contain a responsibility over the program.

What do you mean by responsibility?

According to Martin, responsibility means reason to change and concludes that a class or module should have one and only one reason to be changed (e.g. re written)- (Wikipedia)


2) Usage 

Let’s assume there is a program to generate a PDF file according to the information that are given by the user according to the given format by the program.

So in this scenario ,

Input       –       Details  given by the user according to the format that is provided by the program

Process   –       Generation PDF report

Output    –       PDF report including the details that are entered by the user

Note : There is a one class to generate the report according to a format.

So here the output can be changed according to several reasons,

-          If the user entered different details apart form the format that is given by the program

-          If user wants to send that PDF file to someone through the system apart from downloading it

So here, the thing is do not use the same class to do both changes that I mentioned above. It is a bad approach. Instead of using same class to do both changes we have to use two separate classes for each change or requirement. That’s the usage of Single Responsibility.


3) Example with Violations of Single Responsibility


There is a class called Student.

This example violates Single Responsibility.

Here, Student class is for represent the Student. So Register(),Apply() are responsibilities  of the Student.

So if we want to make changes to these Register or Apply responsibilities, it may be affect to the Student model either by adding an extra properties.

 So when apply the Single Responsibility we have to keep these methods in a separate class.

 


 



So if a class has more than one responsibility, they become coupled. Changes to one responsibility may restrict the class’s ability to meet other requirements.

4) Benefits

  • The class is easier to understand
  • The class is more reusable
  • The class is easier to maintain


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