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Strategy Pattern

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. This pattern allows a client to choose which algorithm to use at runtime.

When to Use:

Use the Strategy pattern when you have multiple algorithms for a specific task and you want to choose the appropriate algorithm at runtime.

Example

// PaymentStrategy Interface
interface PaymentStrategy {
  pay(amount: number): void;
}


// Concrete Strategies
class CreditCardPayment implements PaymentStrategy {
  pay(amount: number): void {
    console.log(`Paid ${amount} using Credit Card`);
  }
}


class PayPalPayment implements PaymentStrategy {
  pay(amount: number): void {
    console.log(`Paid ${amount} using PayPal`);
  }
}


// Context
class PaymentProcessor {
  private strategy: PaymentStrategy;


  constructor(strategy: PaymentStrategy) {
    this.strategy = strategy;
  }


  setStrategy(strategy: PaymentStrategy) {
    this.strategy = strategy;
  }


  processPayment(amount: number) {
    this.strategy.pay(amount);
  }
}


// Usage
const processor = new PaymentProcessor(new CreditCardPayment());
processor.processPayment(100);


processor.setStrategy(new PayPalPayment());
processor.processPayment(150);

Pros:

  • Promotes Open/Closed Principle.
  • Easy to switch between different algorithms.

Cons:

  • Increases the number of classes in the application.
  • Clients must be aware of different strategies.

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