🔹 Domain-Driven Design (DDD) in OOP

**Domain-Driven Design (DDD)** is an **architectural approach** in Object-Oriented Programming (OOP) that focuses on designing software based on **real-world business domains**. It helps in structuring complex applications by aligning the code with real-world concepts.

📌 Why Use DDD?

DDD helps in **building scalable and maintainable applications** by improving how we model business logic.

  • ✅ **Aligns Code with Business Logic** – Models real-world entities accurately.
  • ✅ **Encapsulates Domain Logic** – Ensures domain rules are enforced.
  • ✅ **Improves Collaboration** – Bridges the gap between developers and domain experts.
  • ✅ **Enhances Code Maintainability** – Reduces complexity by organizing code into meaningful components.

📌 Key Concepts in DDD

🔹 1. Entity

An **entity** is an object that has a unique identifier and represents a real-world concept.


            class Order {
                private int orderId;  // Unique identifier
                private String customerName;
            
                public Order(int orderId, String customerName) {
                    this.orderId = orderId;
                    this.customerName = customerName;
                }
            
                public int getOrderId() {
                    return orderId;
                }
            }

🔹 2. Value Object

A **value object** represents an immutable concept that does not have a unique identifier.


            class Address {
                private String city;
                private String country;
            
                public Address(String city, String country) {
                    this.city = city;
                    this.country = country;
                }
            }

🔹 3. Aggregate Root

An **aggregate root** is the main entry point for a group of related objects (entities and value objects).


            class Customer {
                private int id;
                private String name;
                private List orders = new ArrayList<>();
            
                public void addOrder(Order order) {
                    orders.add(order);
                }
            }

🔹 4. Repository

A **repository** handles object persistence and retrieval from a database.


            interface CustomerRepository {
                void save(Customer customer);
                Customer findById(int id);
            }

🔹 5. Service

A **service** contains business logic that does not belong to any single entity.


            class PaymentService {
                public void processPayment(Customer customer, double amount) {
                    System.out.println("Processing payment of $" + amount + " for " + customer.getName());
                }
            }

🎯 Summary

Domain-Driven Design (DDD) **helps structure complex applications** by aligning code with business concepts. Key elements include **Entities, Value Objects, Aggregate Roots, Repositories, and Services**.

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