This guide explains the practical application of core OOP (Object Oriented Programming) concepts—abstraction, encapsulation, inheritance, and polymorphism—through real-world examples. It covers how Agile-Scrum manages projects and how UML diagrams illustrate Object-Oriented Designs for both technical and non-technical stakeholders. It also introduces the practical application of SOLID principles and key design patterns (creational, structural, and behavioral) for building flexible and maintainable software systems.
Here is a mind map illustrating the relationships between OOP Concepts, OO Design Principles, OO Patterns, and their practical application in real-world IT industry projects from a developer/architect's perspective:
mindmap
root((IT Project))
Business Scenario
Requirement Analysis
Functional Requirements
Non-functional Requirements
Constraints
Identifying Domain Entities & Relationships
OOP Concepts
Abstraction
by Specialization
by Generalization
by Aggregation
Encapsulation
Design by Contract
Inheritance
Single
Multiple
Multi-level
Hierarchical
Hybrid
Polymorphism
Planning, Execution & Delivery
Agile Manifesto
Scrum Methodology
Sprint
Sprint Item
SMART
S - Specific
M - Measurable
A - Achievable
R - Relevant
T - Time-bound
Definition of Done
Estimation
Story Points
Fibanocci Estimates
Product Backlog
Product Backlog Item Types
Epic
User Story
Feature
Bug
Spike
Design Change
Requirement Analysis
Minimum Viable Product
Potentially Shippable Product Increment
Agile Ceremonies
Backlog Grooming
Sprint Planning
Daily Standup
Sprint Retrospective
Sprint Demo
Documentation
UML
Use-case Diagram
Entity
Use-case
Actor
Relationship
Association
Actor Generalization
Extend
Include
Use-case Generalization
Class Diagram
Class
Attribute
Method
Stereotype
Entity
Boundary
Control
Interface
Relationship
Dependency
Association
Aggregation
Composition
Generalization
Realization
Design & Implementation
Guidelines
SOLID Principles
S - Single Responsibility
O - Open/Closed
L - Liskov Substitution
I - Interface Segregation
D - Dependency Inversion
Common Reusable Solutions
OO Design Patterns
Creational
Factory Method
Abstract Factory
Singleton
Builder
Prototype
Structural
Adapter
Bridge
Composite
Decorator
Facade
Flyweight
Proxy
Behavioral
Chain of Responsibility
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
Strategy
Template Method
Visitor
Explains practical application of OO Concepts (Abstraction, Encapsulation, Inheritance, and Polymorphism) with day-to-day concrete examples.
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Abstraction: Hiding complex implementation details and showing only essential features.
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Encapsulation: Bundling the data and methods that operate on the data within a single unit (class).
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Inheritance: Mechanism where a new class inherits properties and behavior from an existing class.
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Polymorphism: Ability of different classes to respond to the same method call in different ways.
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Agile-Scrum Methodology
Scrum is an agile process framework for managing complex product development. -
Requirement Analysis with UML Use Case Diagrams
Visualize functional requirements and interactions between the system and users. -
OO Design with UML Class Diagrams
Diagram that represents the structure of the system, showing classes, attributes, methods, and their relationships. -
Mapping UML Class Diagram Relationships into Java Implementation
Mapping associations, compositions, and inheritance into Java code using appropriate keywords.
Please refer to the below article for more details:
https://medium.com/lexicon-digital/inside-the-object-oriented-toolbox-mapping-between-design-implementation-405f00e22bd
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SOLID Principles Explained with Concrete Examples
The SOLID principles are a set of design principles that help software developers design more understandable, flexible, and maintainable code.- S: Single Responsibility Principle
- O: Open/Closed Principle
- L: Liskov Substitution Principle
- I: Interface Segregation Principle
- D: Dependency Inversion Principle
Please refer to the below article for more details:
https://wimal-perera.medium.com/inside-the-object-oriented-toolbox-avoiding-bad-design-with-solid-principles-b8eb256c968c
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How SOLID Principles Are Violated During Early Sprints of an Agile Driven Project
Due to lack of requirement clarity and fast delivery, it is common to see violations of the SOLID principles. -
Achieving Stepwise SOLID Compliance in Already Violated Implementation
Gradual adherence to SOLID principles over successive sprints improves code maintainability.
| Principle | Early Sprint Violations | Steps for Compliance |
|---|---|---|
| S | Classes doing multiple things | Refactor classes to focus on one responsibility |
| O | Code changes require modifying existing classes | Use interfaces and inheritance to extend functionality without altering base classes |
| L | Child class violates base class expectations | Ensure proper override behavior and testing |
| I | Large interfaces with many methods | Break down large interfaces into smaller, focused ones |
| D | High-level modules depend on low-level modules | Introduce dependency injection to reduce coupling |
Please refer to the below article for more details:
https://medium.com/lexicon-digital/developing-agile-driven-software-whilst-adhering-with-best-engineering-practices-261a6aabe7a5
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Introducing Design Patterns (Creational, Structural, and Behavioral)
Design patterns are reusable solutions to common problems in software design. -
In-depth Analysis on Creational Design Patterns
Creational patterns deal with object creation mechanisms, trying to create objects in a manner suitable to the situation.When to use:
- When the system should be independent of how its objects are created, composed, and represented. When not to use:
- When the system doesn't need flexible object creation.
a. Creational Design Patterns
These patterns deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. They provide flexibility in deciding which objects need to be created for a given scenario.
Examples:
- Factory Method
- Abstract Factory
- Singleton
- Builder
- Prototype
b. Structural Design Patterns
These patterns deal with object composition, creating relationships between objects to form larger structures. They help ensure that classes and objects can work together by promoting composability and reusability.
Examples:
- Adapter
- Bridge
- Composite
- Decorator
- Facade
- Flyweight
- Proxy
c. Behavioral Design Patterns
These patterns focus on communication between objects, what happens when objects interact, and how responsibilities are distributed. They define how objects collaborate to fulfill a task.
Examples:
- Chain of Responsibility
- Command
- Interpreter
- Iterator
- Mediator
- Memento
- Observer
- State
- Strategy
- Template Method
- Visitor
| Aspect | Agile | Scrum |
|---|---|---|
| Definition | A set of principles and values for software development, emphasizing flexibility, collaboration, and customer feedback. | A specific Agile framework that provides a structured approach to implementing Agile principles through roles, events, and artifacts. |
| Focus | Agile focuses on continuous improvement, flexibility, and iterative progress. | Scrum focuses on delivering work in short, fixed-length iterations called sprints, typically 2–4 weeks long. |
| Methodology Type | An umbrella term for various frameworks (Scrum, Kanban, XP, etc.) that follow Agile principles. | A specific Agile framework with defined roles, events, and artifacts. |
| Roles | Roles are not defined within the Agile manifesto, and they vary depending on the methodology. | Scrum defines three roles: Product Owner, Scrum Master, and Development Team. |
| Iterations | Iterative approach, but the structure of iterations varies by the Agile methodology. | Scrum follows fixed-length sprints (typically 2–4 weeks). |
| Flexibility | Agile encourages flexibility in processes to adapt to changing requirements. | Scrum follows strict guidelines, but it’s flexible in terms of adapting to changing requirements during sprints. |
| Planning | Agile emphasizes adaptive planning throughout the project life cycle. | Scrum involves detailed planning in the form of sprint planning, backlog grooming, and sprint reviews. |
| Team Size | Agile teams are typically small, but there’s no specific size. | Scrum teams usually consist of 3 to 9 people. |
| Customer Interaction | Frequent customer collaboration and feedback are central to Agile. | Scrum incorporates feedback through reviews at the end of each sprint and maintains close communication with the Product Owner. |
| Agile Manifesto | The Agile Manifesto focuses on values and principles that promote Agile development. | Scrum aligns with the values of the Agile Manifesto but provides more structure and specific guidelines for implementing Agile. |
The Agile Manifesto outlines the core values and principles behind Agile methodologies. It was created in 2001 by 17 software developers to promote a better way of developing software. The manifesto emphasizes:
- Individuals and interactions over processes and tools.
- Working software over comprehensive documentation.
- Customer collaboration over contract negotiation.
- Responding to change over following a plan.
You can find the full Agile Manifesto and its principles here.