public double calculateDiscount(String customerType, double amount) {
    if (customerType.equals("regular")) {
        return amount * 0.05;
    } else if (customerType.equals("vip")) {
        return amount * 0.1;
    } else if (customerType.equals("super-vip")) {
        return amount * 0.2;
    } else {
        return 0;
    }
}

public interface DiscountStrategy {
    double applyDiscount(double amount);
}

public class RegularDiscount implements DiscountStrategy {
    public double applyDiscount(double amount) {
        return amount * 0.05;
    }
}

public class VipDiscount implements DiscountStrategy {
    public double applyDiscount(double amount) {
        return amount * 0.1;
    }
}

public class SuperVipDiscount implements DiscountStrategy {
    public double applyDiscount(double amount) {
        return amount * 0.2;
    }
}

public class DiscountService {
    private final DiscountStrategy strategy;

    public DiscountService(DiscountStrategy strategy) {
        this.strategy = strategy;
    }

    public double getDiscountedPrice(double amount) {
        return strategy.applyDiscount(amount);
    }
}

DiscountStrategy strategy = new VipDiscount(); 
DiscountService service = new DiscountService(strategy);

double price = service.getDiscountedPrice(1000); // 100.0

Map<String, DiscountStrategy> strategies = Map.of(
    "regular", new RegularDiscount(),
    "vip", new VipDiscount(),
    "super-vip", new SuperVipDiscount()
);

DiscountStrategy strategy = strategies.getOrDefault(customerType, amount -> 0.0);
double result = strategy.applyDiscount(1000);

String greeting = "Hello, World!";

void main() {
    System.out.println(greeting);
}