The SOLID Principles are the design principles that enable us to manage several software design problems. These principles provide us with ways to move from tightly coupled code to loosely coupled and encapsulated real business needs properly. Also, readable, adaptable, and scalable code.
The SOLID Principles guide developers as they write readable, adaptable, and scalable code or design an application.
The SOLID Principles can be applied to any OOP program.
The SOLID Principles were developed by computer science instructor and author Robert C. Martin.
Now, the SOLID Principles have also been adopted in both agile development and adaptive software development.
The 5 principles of SOLID are:
1. Single Responsibility Principle (SRP)
2. Open-Closed Principle (OCP)
3. Liskov Substitution Principle (LSP)
4. Interface Segregation Principle (ISP)
5. DependencyInversion Principle (DIP)
Single Responsibility Principle (SRP) is one of the SOLID principles that states a class, module, or function should have only one reason to change.
Implementation:
Let us look at an example of how SRP can be applied to make our
EmployeeService class more readable.
// Does not follow a
Single-responsibility principle (SRP)
public class EmployeeService
{
public void Register(string eployeename)
{
//Employee
name restrictions
if (eployeename == "admin")
throw new InvalidOperationException();
//Insert
employee into database.
SqlConnection connection = new
SqlConnection();
connection.Open();
SqlCommand command = new SqlCommand("INSERT INTO [...]");
//Send
a welcome email to employee.
SmtpClient client = new SmtpClient("smtp.emailhost.com");
client.Send(new
MailMessage());
}
}
The program above does not follow the Single-responsibility principle
(SRP) because EmployeeService does three different jobs:
1. Register an
employee,
2. Connect to
the database to insert the employee’s name
3. Send a
welcome email to the employee
This type of class would create confusion in larger projects
because all the above 3 features are in the same class. So, we need to split the class
into three specific classes that will do a single job.
Now all other jobs refactored to separate classes
1. EmployeeService
class
2. EmployeeRepository
class
3. EmailService
class
The code looks like this,
public class EmployeeService
{
public void Register (string eployeename)
{
//Employee
name restrictions
if (eployeename == "admin")
throw new InvalidOperationException();
//Insert
employee into database.
_userRepository.Insert(...);
//Send
a welcome email to employee.
_emailService.Send(...);
}
}
This achieves the SRP because EmployeeService only registers an
employee and the only reason it would change is if more eployeename
restrictions were added. All other behaviors are maintained in the program but
are now achieved with calls to EmployeeRepository and EmailService.
Advantages of the Single Responsibility Principle:
1. Increased
Code Reusability
2. Reduce
code Complexity
3. Clearer
Design
4. Easier
Testing
5. Enhanced
Readability and Maintainability
6. Clearer
Design
Disadvantages of the Single
Responsibility Principle:
1. Increased
the Number of Classes: SRP may lead to a larger number of smaller classes, each
responsible for a specific task. This can sometimes make the codebase feel more
fragmented and complex.
2. Potential
Overhead: Breaking down responsibilities into small, focused classes might
introduce some overhead.
When to
use the Single Responsibility Principle:
Remember, the goal is to design classes that are focused on a
single responsibility. When a class has multiple reasons to change, it becomes
more difficult to maintain, test, and understand. Applying SRP leads to more
modular, maintainable, and flexible code.