Adapter Pattern

// ========== Target Interface (what our system expects) ==========
interface PaymentProcessor {
    void pay(String orderId, double amount);
    boolean refund(String transactionId);
}

// ========== Adaptee (third-party payment gateway with different interface) ==========
class StripeGateway {
    public String createCharge(double amountInCents, String currency, String description) {
        System.out.println("Stripe: Charging " + amountInCents + " cents");
        return "ch_" + System.currentTimeMillis();
    }
    
    public boolean reverseCharge(String chargeId) {
        System.out.println("Stripe: Reversing charge " + chargeId);
        return true;
    }
}

// ========== Adapter ==========
class StripeAdapter implements PaymentProcessor {
    private StripeGateway stripe;
    
    public StripeAdapter(StripeGateway stripe) {
        this.stripe = stripe;
    }
    
    @Override
    public void pay(String orderId, double amount) {
        // Convert dollars to cents, adapt interface
        long amountInCents = Math.round(amount * 100);
        String description = "Order: " + orderId;
        stripe.createCharge(amountInCents, "USD", description);
    }
    
    @Override
    public boolean refund(String transactionId) {
        // Adapt method name
        return stripe.reverseCharge(transactionId);
    }
}

// ========== Another Adaptee ==========
class PayPalSDK {
    public void sendPayment(String recipient, double amount) {
        System.out.println("PayPal: Sending $" + amount);
    }
    
    public void cancelPayment(String paymentId) {
        System.out.println("PayPal: Cancelling " + paymentId);
    }
}

// ========== Another Adapter ==========
class PayPalAdapter implements PaymentProcessor {
    private PayPalSDK paypal;
    
    public PayPalAdapter(PayPalSDK paypal) {
        this.paypal = paypal;
    }
    
    @Override
    public void pay(String orderId, double amount) {
        paypal.sendPayment("merchant@store.com", amount);
    }
    
    @Override
    public boolean refund(String transactionId) {
        paypal.cancelPayment(transactionId);
        return true;
    }
}

// ========== Client Code ==========
public class Main {
    public static void main(String[] args) {
        // Client code works with any PaymentProcessor
        PaymentProcessor processor;
        
        // Use Stripe
        processor = new StripeAdapter(new StripeGateway());
        processor.pay("ORDER-123", 99.99);
        
        // Switch to PayPal - same interface!
        processor = new PayPalAdapter(new PayPalSDK());
        processor.pay("ORDER-456", 49.99);
    }
}