Java Code Style Standards

This rule applies to files matching the patterns above.

# Java Code Style Standards

## Rule
All Java code MUST follow Google Java Style Guide formatting. Use PascalCase for classes, camelCase for methods and variables, UPPER_SNAKE_CASE for constants.

## Naming Conventions
| Element | Convention | Example |
|---------|-----------|---------|
| Class | PascalCase | `UserService`, `HttpClient` |
| Method | camelCase, verb prefix | `getUserById()`, `isValid()` |
| Variable | camelCase | `userName`, `orderCount` |
| Constant | UPPER_SNAKE_CASE | `MAX_RETRY_COUNT`, `DEFAULT_TIMEOUT` |
| Package | all lowercase | `com.myapp.user`, `org.example.auth` |
| Interface | PascalCase (no I prefix) | `Repository`, `Validator` |
| Enum | PascalCase, values UPPER_SNAKE | `OrderStatus.PENDING` |

## Good Examples
```java
package com.myapp.order;

import java.util.List;
import java.util.Optional;

public class OrderService {
    private static final int MAX_RETRY_COUNT = 3;
    private static final Duration DEFAULT_TIMEOUT = Duration.ofSeconds(30);

    private final OrderRepository orderRepository;
    private final PaymentGateway paymentGateway;

    public OrderService(OrderRepository orderRepository, PaymentGateway paymentGateway) {
        this.orderRepository = orderRepository;
        this.paymentGateway = paymentGateway;
    }

    public Optional<Order> findById(String orderId) {
        return orderRepository.findById(orderId);
    }

    public Order createOrder(CreateOrderRequest request) {
        validateRequest(request);
        Order order = Order.from(request);
        return orderRepository.save(order);
    }

    private void validateRequest(CreateOrderRequest request) {
        if (request.items().isEmpty()) {
            throw new IllegalArgumentException("Order must have at least one item");
        }
    }
}
```

## Bad Examples
```java
// BAD: Wrong naming conventions
public class order_service {           // Should be PascalCase
    private int MAXRETRY = 3;          // Should be MAX_RETRY or maxRetry
    public void GetUser() { ... }      // Should be getUser()
    String user_name;                  // Should be userName
}

// BAD: I-prefix on interfaces (this is C#, not Java)
public interface IUserRepository { ... }  // Just UserRepository

// BAD: Wildcard imports
import java.util.*;                    // Import specific classes
```

## Enforcement
- Use google-java-format: `google-java-format --replace src/**/*.java`
- Configure Checkstyle with Google style rules
- IDE: IntelliJ/Eclipse Google Style formatter profile
- CI: `mvn checkstyle:check` or `gradle checkstyleMain`