b_OCP

Open/Closed Principle (OCP)

📖 What is OCP?

The Open/Closed Principle (OCP) states:

Code should be open for extension but closed for modification.

This means you should be able to add new functionality without changing existing code.

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❌ Before (OCP Violation)

The PaymentService uses multiple if-else or switch statements to process different payment methods.

if (paymentType.equals("CARD")) {
    ...
} else if (paymentType.equals("UPI")) {
    ...
} else if (paymentType.equals("PAYPAL")) {
    ...
}

Whenever a new payment method is added, the existing class must be modified.

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✅ After (OCP Followed)

Each payment method has its own implementation.

• Payment → Interface
• CardPayment → Processes Card payments
• UpiPayment → Processes UPI payments
• PaypalPayment → Processes PayPal payments

To add a new payment method (e.g., CryptoPayment), simply create a new class that implements the PaymentService interface.

No existing code needs to be changed.

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📂 Project Structure

b_OCP
│
├── before/
│   └── OCP Violation
│
├── after/
│   └── OCP Implementation
│
└── README.md

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🎯 Benefits of OCP

• Easy to add new features
• Reduces modification of existing code
• Improves maintainability
• Supports scalability
• Encourages the use of polymorphism

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💡 Real-World Example

Think of an online payment gateway.

Initially, it supports:

• 💳 Card Payment

Later, the company wants to add:

• 📱 UPI Payment
• 🅿️ PayPal
• 💰 Crypto Payment

Instead of modifying the existing payment logic every time, simply create a new payment class for each new payment method.

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🚀 Key Takeaway

Extend the system by adding new classes, not by modifying existing ones.