Behavioral_Strategy Pattern

✅ Strategy Pattern

• make a lot of algorithms
• encapsulate them
• and make them interchangeable at runtime, 갈아끼우기
• client will use the common interface only
• actual behavior can vary according to the selected strategy
• 👍🏻 algorithm is independent from the client that uses it
• 👍🏻 no need to use if/else, switch

✅ Diagram

👀

👎🏻 before

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

✔️ Strategy interface

public interface PaymentStrategy {
    void pay(double amount);
}

✔️ Concrete strategies

• card payment method
• paypal payment method

public class CreditCardPayment implements PaymentStrategy {

    @Override
    public void pay(double amount) {
        //pay w credit card
    }
}

public class PaypalPayment implements PaymentStrategy {

    @Override
    public void pay(double amount) {
        //pay w paypal
    }
}

✔️ Context

• has strategy interface as field

public class PaymentService {

    private PaymentStrategy paymentStrategy;

    public PaymentService(PaymentStrategy paymentStrategy) { //interchange, 갈아끼우기 method
        this.paymentStrategy = paymentStrategy;
    }

    public void processPayment(double amount) {
        paymentStrategy.pay(amount);
    }
}

✔️ Client

public class Main {

    public static void main(String[] args) {

        PaymentService service1 = new PaymentService( new CreditCardPayment()); //use card payment method
        service1.processPayment(100);

        PaymentService service2 = new PaymentService( new PaypalPayment()); //use paypal method
        service2.processPayment(100);
    }
}

🛠️

• used for Dependency injections