3.4. Code Writing Rules

3.4.1. Access Modifiers

• Class fields must default to private.
• Provide public methods only when external access is required.
• Classes used only within the package must be declared as package-private (omit the access modifier).

3.4.2. Import Rules

• Wildcard imports (import java.util.*) must not be used.
• Unused imports must be removed.
• Google Java Format handles import ordering automatically.

3.4.3. No Magic Numbers

Literal values must not be used directly in code. Define them as constants to clarify their meaning.

// Bad
if (retryCount > 3) { ... }

// Good
private static final int MAX_RETRY_COUNT = 3;

if (retryCount > MAX_RETRY_COUNT) { ... }

3.4.4. Optional Usage Rules

• Use Optional as a return type. Do not use it for fields or parameters.
• Do not call Optional.get() directly. Use orElseThrow(), orElse(), or ifPresent() instead.

// Bad
UsersRecord record = userRepository.findById(id).get();

// Good
UsersRecord record = userRepository.findById(id)
    .orElseThrow(() -> new UserNotFoundException(id));

3.4.5. Null Handling

• Do not return null. Use empty collections (Collections.emptyList()) or Optional instead.
• Use Objects.requireNonNull() for null checks on parameters.
• Actively use @Nullable and @NonNull annotations.

3.4.6. String Handling

• Use String.format() or text blocks (""") instead of the + operator for string concatenation.
• Use String.isEmpty() or String.isBlank() for empty string comparison.