SOLID refers to five fundamental principles used in software design. These principles ensure that software is more flexible, maintainable, and testable.
The SOLID principles are as follows:
S: Single Responsibility Principle (SRP): A class should have only one responsibility. It ensures that classes are more understandable and manageable.
public class UserService {
private final UserRepository userRepository;
public UserService(UserRepository userRepository) {
this.userRepository = userRepository;
}
public void createUser(String name) {
userRepository.save(name);
}
}
O: Open/Closed Principle (OCP): Classes should be open for extension but closed for modification. It allows you to add new functionality without changing existing code.
public interface Shape {
double area();
}
public class Circle implements Shape {
private final double radius;
public Circle(double radius) {
this.radius = radius;
}
@Override
public double area() {
return Math.PI * radius * radius;
}
}
public class Rectangle implements Shape {
private final double width;
private final double height;
public Rectangle(double width, double height) {
this.width = width;
this.height = height;
}
@Override
public double area() {
return width * height;
}
}
L: Liskov Substitution Principle (LSP): Derived classes should be substitutable for their base classes. It ensures that objects can be used interchangeably.
abstract class FlyingBird{
abstract void fly();
}
abstract class NonFlyingBird{
abstract void doSomething();
}
class Eagle extends FlyingBird {
@Override
public void fly() {
// implement something
}
}
class Ostrich extends NonFlyingBird {
@Override
public void doSomething() {
// implement something
}
}
I: Interface Segregation Principle (ISP): Users should not be forced to depend on interfaces they do not use. It ensures that interfaces are more specific and understandable.
interface IAreaCalculator {
double calculateArea();
}
interface IVolumeCalculator {
double calculateVolume();
}
class Square implements IAreaCalculator {
@Override
public double calculateArea() {
// calculate the area
}
}
class Cube implements IAreaCalculator, IVolumeCalculator {
@Override
public double calculateArea() {
// calculate the area
}
@Override
public double calculateVolume() {
// calculate the volume
}
}
D: Dependency Inversion Principle (DIP): High-level modules should not depend on low-level modules. Both should depend on abstractions. This reduces dependencies and increases testability.
class UserService {
private final UserRepository userRepository;
public UserService(UserRepository userRepository) {
this.userRepository = userRepository;
}
public void createUser(String name) {
userRepository.save(name);
}
}
class CourseService {
private final UserService userService;
public CourseService(UserService userService) {
this.userService = userService;
}
public void createCourse(String name) {
// implementation
}
}
| Keyword | Description |
|---|---|
| Coupling | The degree of interdependence between software modules. Low coupling is preferred for modularity and maintainability. |
| Cohesion | The degree to which the elements of a module belong together. High cohesion is desired for clarity and focus. |
| Single Responsibility Principle (SRP) | A class should have only one responsibility. It ensures that classes are more understandable and manageable. |
| Open/Closed Principle (OCP) | Classes should be open for extension but closed for modification. It allows adding new functionality without changing existing code. |
| Liskov Substitution Principle (LSP) | Derived classes should be substitutable for their base classes. It ensures objects can be used interchangeably. |
| Interface Segregation Principle (ISP) | Users should not be forced to depend on interfaces they do not use. It ensures interfaces are more specific and understandable. |
| Dependency Inversion Principle (DIP) | High-level modules should not depend on low-level modules. Both should depend on abstractions. This reduces dependencies and increases testability. |
Thank you for your interest in the SOLID principles! For more insights and resources, feel free to check out https://dub.sh/burakboduroglu.
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