Unraveling the Strategy Design Pattern: A Guide to SOLID Principle

In the vast landscape of software design, the Strategy Design Pattern emerges as a powerful ally, bringing flexibility, maintainability, and adherence to the Open/Closed Principle. In this blog post, we’ll embark on a journey to understand the Strategy Pattern, explore its use cases, delve into its benefits, and appreciate its synergy with the Open/Closed Principle.

What is the Strategy Design Pattern?

The Strategy Design Pattern is a behavioral pattern that enables a class to define a family of algorithms, encapsulate each one of them, and make them interchangeable. By encapsulating algorithms into separate classes, the Strategy Pattern allows clients to choose an algorithm at runtime without altering the client’s code. This promotes code reuse, modularity, and easy extensibility.

When to Use the Strategy Pattern?

The Strategy Pattern proves its worth in several scenarios:

1. Multiple Algorithms: When an application needs to support multiple algorithms or variations of an algorithm, the Strategy Pattern provides an elegant solution by encapsulating each algorithm in its own strategy class.
2. Runtime Algorithm Selection: If the choice of an algorithm needs to be determined dynamically at runtime, the Strategy Pattern shines. It allows for flexibility in choosing algorithms based on changing conditions.
3. Algorithm Variants: When there are several variants of an algorithm and a class needs to support different variants, the Strategy Pattern helps by encapsulating each variant in a separate strategy.
4. Avoiding Conditional Statements: The Strategy Pattern is particularly beneficial in scenarios where conditional statements are used to switch between different behaviors. It replaces these conditionals with a cleaner, more extensible solution.
5. Multiple Serializer: The Strategy pattern can also be used when you have multiple serializer methods for the object and depending on the input you want to serialize the object.

Benefits of the Strategy Pattern

1. Flexibility and Extensibility:

The Strategy Pattern provides a flexible framework that allows new algorithms to be added without modifying existing code. It’s easy to extend and add new strategies, promoting a more modular and scalable system.

2. Code Reusability:

By encapsulating algorithms into separate classes, the Strategy Pattern encourages code reuse. Each strategy class can be reused in different contexts, reducing duplication and promoting maintainability.

3. Improved Testability:

Strategies can be tested independently, making it easier to ensure the correctness of each algorithm. This modularity enhances the overall testability of the codebase.

Strategy Pattern and the Open/Closed Principle

The Open/Closed Principle, one of the SOLID principles of object-oriented design, states that a class should be open for extension but closed for modification. The Strategy Pattern perfectly aligns with this principle, allowing for the addition of new strategies without altering existing code.

By encapsulating algorithms in separate strategy classes, new strategies can be introduced by creating new classes that adhere to the same interface. This conforms to the Open/Closed Principle, as the existing code remains untouched while the system gets extended with new strategies.

Let's suppose you want to Create a Payment Service and currently you have to process payment using Paypal and Bank Transfer. But in the Future there could be more Payment Methods. I will show you code that you will think at first glance which is not a recommended way.

now let's see how we can make it better using strategy design pattern.

Implementing the Strategy Pattern

Let’s take a brief look at a simple Payment Processor example in JavaScript to understand the Strategy Pattern in action:

// Define Payment interface
interface Payment {
  process(amount: number): void;
}

// Create Paypal class implementing Payment interface
class Paypal implements Payment {
  constructor(private amount: number) {
    // Constructor logic if needed
  }

  process() {
    console.log(`Paypal: ${this.amount}`);
    // Processing logic for Paypal
  }
}

// Create BankTransfer class implementing Payment interface
class BankTransfer implements Payment {
  constructor(private amount: number) {
    // Constructor logic if needed
  }

  process() {
    console.log(`BankTransfer: ${this.amount}`);
    // Processing logic for BankTransfer
  }
}

// Define PaymentType object with corresponding classes
const PaymentType = {
  PAYPAL: Paypal,
  BANK_TRANSFER: BankTransfer,
};

// Create PaymentStrategy class
class PaymentStrategy {
  constructor(private paymentType: keyof typeof PaymentType) {}

  // Process method to instantiate the chosen Payment class
  process(amount: number): Payment | null {
    const SelectedPaymentClass = PaymentType[this.paymentType];

    // Check if the selected payment type is valid
    if (SelectedPaymentClass) {
      // Instantiate the chosen Payment class and return it
      return new SelectedPaymentClass(amount);
    } else {
      console.error('Invalid payment type');
      return null;
    }
  }
}

// Example usage
const PaymentProcessor = new PaymentStrategy('PAYPAL');
const paymentObject = PaymentProcessor.process(123);

Conclusion

The Strategy Design Pattern emerges as a key player in creating adaptable, scalable, and maintainable software systems. By encapsulating algorithms into separate classes, the Strategy Pattern fosters flexibility and extensibility while seamlessly adhering to the Open/Closed Principle. As we continue to explore design patterns in future blog posts, the Strategy Pattern will undoubtedly stand as a fundamental tool in the arsenal of every discerning software developer. Stay tuned for more insights into the world of design patterns and their practical applications!