When to use the Strategy pattern?

When to Use the Strategy Pattern: A Comprehensive Guide

The Strategy pattern is a behavioral design pattern that enables selecting an algorithm’s behavior at runtime. It’s particularly useful when you have multiple algorithms for a specific task and want to switch them seamlessly. This pattern promotes flexibility and reusability in your code, making it easier to maintain and extend.

What is the Strategy Pattern?

The Strategy pattern allows you to define a family of algorithms, encapsulate each one, and make them interchangeable. This pattern enables the algorithm to vary independently from the clients that use it. By encapsulating the algorithm, you can easily swap one strategy for another without altering the client code.

Why Use the Strategy Pattern?

The Strategy pattern is beneficial in scenarios where you need:

Multiple algorithms: When a task can be performed using different methods, and you want to switch between them easily.
Runtime flexibility: When the choice of algorithm needs to be made at runtime, rather than at compile time.
Code maintenance: To keep the code clean and manageable by avoiding conditional statements scattered throughout your codebase.

Key Benefits of the Strategy Pattern

Implementing the Strategy pattern offers several advantages:

Improved Code Organization: By separating the algorithm from client code, you enhance readability and organization.
Enhanced Flexibility: You can add new strategies without modifying the existing code, adhering to the Open/Closed Principle.
Simplified Testing: Each strategy can be tested independently, ensuring robust and reliable code.

How to Implement the Strategy Pattern

To implement the Strategy pattern, follow these steps:

Define a Strategy Interface: Create an interface to represent the strategy. This interface declares the method that all concrete strategies will implement.
Create Concrete Strategies: Implement the strategy interface in concrete classes, each representing a different algorithm.
Context Class: Develop a context class that maintains a reference to a strategy object. This class will delegate the task to the strategy object.
Client Code: The client code will configure the context with a desired strategy and execute the algorithm through the context.

Example of the Strategy Pattern

Consider a payment processing system that supports multiple payment methods like credit card, PayPal, and Bitcoin. The Strategy pattern can help manage these methods efficiently.

// Strategy Interface
interface PaymentStrategy {
    void pay(int amount);
}

// Concrete Strategy for Credit Card Payment
class CreditCardPayment implements PaymentStrategy {
    public void pay(int amount) {
        System.out.println("Paid " + amount + " using Credit Card.");
    }
}

// Concrete Strategy for PayPal Payment
class PayPalPayment implements PaymentStrategy {
    public void pay(int amount) {
        System.out.println("Paid " + amount + " using PayPal.");
    }
}

// Context Class
class ShoppingCart {
    private PaymentStrategy paymentStrategy;

    public void setPaymentStrategy(PaymentStrategy paymentStrategy) {
        this.paymentStrategy = paymentStrategy;
    }

    public void checkout(int amount) {
        paymentStrategy.pay(amount);
    }
}

// Client Code
public class Main {
    public static void main(String[] args) {
        ShoppingCart cart = new ShoppingCart();
        
        // Pay using Credit Card
        cart.setPaymentStrategy(new CreditCardPayment());
        cart.checkout(100);
        
        // Pay using PayPal
        cart.setPaymentStrategy(new PayPalPayment());
        cart.checkout(200);
    }
}

When Should You Use the Strategy Pattern?