This presentation provides a comprehensive overview of the SOLID principles—five key design principles that help developers create more maintainable, flexible, and scalable object-oriented software. Each principle is broken down with clear explanations, real-world analogies, and practical code examples to aid understanding. Whether you're a beginner or an experienced developer, this presentation will strengthen your grasp of clean code practices and object-oriented programming design patterns.

1. SOLID
PRINCIPLES
By Jyothish Ramachandran
MCA First Year
IN OOPS

2. SOLID PRINCIPLES: BUILDING MAINTAINABLE AND
EXTENSIBLE CODE
Q. What is SOLID?
• Acronym for Single Responsibility, Open-Closed, Liskov Substitution,
Interface Segregation, and Dependency Inversion principles.
• A set of design principles for object-oriented programming (OOP).
02
Q. Why SOLID Matters
• Maintainability: Makes code easier to understand and modify.
• Extensibility: Promotes code that can be easily expanded without breaking
existing functionality.
• Testability: Improves code testability.
• Readability: Enhances code readability and understanding.

3. SOLID
PRINCIPLE
1
2
3
4
5
Single Responsibility Principle
Open-Closed Principle
Liskov Substitution Principle
Interface Segregation Principle
Dependency Inversion Principle

4. SINGLE RESPONSIBILITY
PRINCIPLE (SRP)
Each module /class/ function in a competition program should be
responsible for a single, well-defined part of that program's
functionality. They should encapsulate that part and their services
should be narrowly aligned with that responsibility."
Benefits
• Maintainability: Easier to understand and modify.
• Testability: Easier to write unit tests.
• Decoupling: Reduces dependencies between classes.
A PERSON JUGGLING MULTIPLE
BALLS, STRUGGLING TO KEEP THEM
ALL IN THE AIR

5. OPEN-CLOSED PRINCIPLE
The Open-Closed Principle (OCP) states that software entities (like classes,
modules, or functions) should be designed in a way that allows new
functionality to be added without modifying their existing code.
Benefits
• Maintainability: Easier to add new features without modifying
existing code.
• Extensibility: Promotes flexibility and adaptability.
• Testability: Improves code testability.
LEGO BRICKS ARE MODULAR,
ALLOWING FOR EASY EXTENSION
WITHOUT MODIFYING EXISTING
PARTS.

6. The Liskov Substitution Principle (LSP) is a fundamental principle in object-
oriented programming (OOP) that states: if S is a subtype of T, then objects
of type T should be replaceable with objects of type S without affecting the
correctness of the program.
Benefits
• Clarity: The sentence is more concise and easier to understand.
• Specificity: The terms "subtype" and "correctness of the program" are
used to clarify the principle.
• Conciseness: The phrase "replaceable with objects of type S" is used
instead of "should be replaced with object of type S" for better clarity
and conciseness.
LISKOV SUBSTITUTION
PRINCIPLE (LSP)
A car rental company can assign you any
vehicle (bike, car, or bus), and each vehicle
should seamlessly replace another,
ensuring you can reach your destination
without altering the expected functionality.

7. INTERFACE SEGREGATION
PRINCIPLE (ISP)
The Interface Segregation Principle (ISP) states that clients should not be
forced to implement methods they do not use. Instead of creating a single,
large interface, multiple smaller interfaces can be defined to provide a more
granular level of functionality. This ensures that classes only implement
methods they need, reducing unnecessary coupling and improving code
maintainability.
Benefits
• Decoupling: Reduces dependencies between classes.
• Maintainability: Makes code easier to maintain and extend.
• Testability: Improves code testability.
A PERSON SORTING THROUGH A PILE
OF TRASH, SEPARATING IT INTO
DIFFERENT RECYCLING BINS LABELED
"PAPER," "PLASTIC," "GLASS," AND
"ORGANIC."

8. The Dependency Inversion Principle (DIP) states that high-level modules
should not depend on low-level modules. Both high-level and low-level
modules should depend on abstractions. Abstractions should not depend
on details. Details should depend on abstractions. Always strive to keep
high-level and low-level modules as loosely coupled as possible.
Benefits
• Decoupling: Reduces dependencies between modules.
• Flexibility: Makes code more flexible and adaptable to change.
• Testability: Improves code testability.
DEPENDENCY INVERSION
PRINCIPLE (DIP)
A PYRAMID WITH A WIDE BASE (LOW-LEVEL
MODULES) SUPPORTING A NARROW TOP
(HIGH-LEVEL MODULES)

9. TECHNICAL EXAMPLES OF EACH
PRINCIPLE
• Single Responsibility Principle (SRP)
Example: A Calculator class should only handle mathematical operations. Input validation
should be handled by a separate InputValidator class.
• Open-Closed Principle (OCP)
Example: A Shape base class can be extended with new shape types (e.g., Circle,
Rectangle, Triangle) without modifying the base class.
• Liskov's Substitution Principle
Example: Liskov Substitution Principle (LSP) Example:
If a Rectangle class is extended by a Square class, the Square should be able to
replace the Rectangle without altering the correctness of the program.

10. TECHNICAL EXAMPLES OF EACH
PRINCIPLE
• Interface Segregation Principle (ISP)
Example: Each application implements on smartphones hasspecific, focused
interfaces based on its functionality (e.g., a Messaging App interface for
messaging and a Camera App interface for photo and video capture), ensuring
that applications only depend on the methods they need, avoiding unnecessary
or unrelated functionality.
• Dependency Inversion Principle
Example: In a vehicle system, the Car class should depend on an
abstraction Engine rather than a concrete class like DieselEngine,
allowing easy swapping of different engine types (e.g.,
PetrolEngine, ElectricEngine).

11. THANK YOU