SOLID Principle C#
What is SOLID Principle?
'In object-oriented computer programming, SOLID is a mnemonic acronym for five design principles intended to make software designs more understandable, flexible and maintainable.'
SOLID is an acronym for the following.
S: Single Responsibility Principle (SRP)
O: Open-closed Principle (OCP)
L: Liskov substitution Principle (LSP)
I: Interface Segregation Principle (ISP)
D: Dependency Inversion Principle (DIP)
S: Single Responsibility Principle (SRP)
SRP says, "Every software module should have only one reason to change.".
Any class must have one and only one reason to change. In other words, a class must only have a single responsibility. This principle is simple, but not always easy to follow
Example
class Customer {
public function createCustomer(Request $request)
{ // Create customer
}
}
class Order {
public function submitOrder (Request $request)
{ // Submit Orders
}
}
O: Open/Closed Principle
The Open/closed Principle says, "A software module/class is open for extension and closed for modification."
Objects or entities must be open for extension but closed for modification. A class must be easily extensible without requiring modification of the class itself. The goal of this principle is to help create well-encapsulated, highly cohesive systems.
Example
interface ISavingAccount {
public function CalculateInterest();
}
class RegularSavingAccount implements ISavingAccount {
public function CalculateInterest()
{
//Calculate interest for regular saving account
}
}
class SalarySavingAccount implements ISavingAccount {
public function CalculateInterest()
{
//Calculate interest for regular saving account
}
}
L: Liskov Substitution Principle
The Liskov Substitution Principle (LSP) states, "you should be able to use any derived class instead of a parent class and have it behave in the same manner without modification.".
Derived types must be completely substitutable for their base types. New derived classes must just extend without replacing the functionality of old classes.
Example
class Bird{
// Methods related to birds
}
class FlyingBirds extends Bird
{
public function Fly()
{
Return “I can Fly”;
}
}
class Ostrich extends Bird
{
// Methods related to birds
}
I: Interface Segregation Principle (ISP)
The Interface Segregation Principle states "that clients should not be forced to implement interfaces they don't use. Instead of one fat interface, many small interfaces are preferred based on groups of methods, each serving one submodule.".
Clients must not be dependent upon interfaces or methods they don't use. Keeping interfaces segregated helps a developer more easily know which one to call for specific functions and helps us avoid fat or polluted interfaces that can affect the performance of a system.
Example
interface OnlineClientInterface
{
public function acceptOnlineOrder();
public function payOnline();
}
interface WalkInCustomerInterface
{
public function walkInCustomerOrder();
public function payInPerson();
}
class OnlineClient implements OnlineClientInterface
{
public function acceptOnlineOrder()
{
//logic for placing online order
}
public function payOnline()
{
//logic for paying online
}
}
class WalkInCustomer implements WalkInCustomerInterface
{
public function walkInCustomerOrder()
{
//logic for walk in customer order
}
public function payInPerson()
{
//logic for payment in person
}
}
D: Dependency Inversion Principle
The Dependency Inversion Principle (DIP) states that high-level modules/classes should not depend on low-level modules/classes. First, both should depend upon abstractions. Secondly, abstractions should not rely upon details. Finally, details should depend upon abstractions.
This principle helps maintain a system that’s properly coupled. Avoiding high-level class dependencies on low-level classes helps keep a system flexible and extensible.
Example
interface EBook
{
function read();
}
class PDFBook implements EBook
{
function read()
{
return "reading a pdf book.";
}
}
class EBookReader {
private $book;
function __construct(EBook $book) { $this->book = $book; } function read() { return $this->book->read(); }
}
$book = new PDFBook();
$read = new EBookReader($b);
$read->read();
Conclusion:
Using SOLID principles is critical to being a really good developer and creating valuable software solutions. SOLID is essentially a balanced nutrition plan for software development. When we don’t use these principles in development, our code base becomes bloated and overweight. The system then requires extra work and attention to “trim down” or even maintain, and is at much higher risk for an emergency scare.