java-coding-style

name	java-coding-style
description	MANDATORY MASTER skill for Java coding style. Enforces Checkstyle (4 spaces, K&R braces), strict Javadoc templates, utility class boundaries, and functional programming patterns (In-Memory JOIN, Cursor Batching).

Java Coding Style & Utility Standards

Trigger: You MUST read and follow this guide when writing, formatting, or reviewing ANY Java code to ensure structural and stylistic consistency.

💅 1. Formatting & Naming Conventions

BASE RULE: This project strictly enforces a combination of Google Java Style and Sun Code Conventions. When in doubt about formatting, default to Google Java Style.

• Indentation: ALWAYS use 4 spaces. NEVER use tabs.
• Line Wrapping: Wrap before the . operator for chained methods (e.g., Stream API, MyBatis wrappers).
• Braces (K&R Style):
  • Opening brace { on the same line.
  • Closing brace } on a new line.
  • ALWAYS use braces for if, else, for, while (no single-line omissions).
• Imports: NO wildcard imports (import java.util.*; is strictly forbidden).
• Naming:
  • Classes/Interfaces: UpperCamelCase. Implementations MUST use the Impl suffix.
  • Methods/Variables: lowerCamelCase.
  • Constants: UPPER_SNAKE_CASE.

---

📝 2. Javadoc & Comments Standard

EVERY public element MUST have Javadoc. Do not use single-line // for structural comments.

Class-Level Javadoc (Required for all Controllers, Services, Entities):

/**
 * One-line description of the class responsibility
 *
 * @author HeHui
 * @date 2026-03-31
 */

Method-Level Javadoc (Required for all public methods):

/**
 * Method description
 *
 * @param request    Request payload description
 * @param accessUser Current logged-in user context
 *
 * @return {@link ApiResponse}<{@link Void}>
 */

Field-Level Javadoc (Required for ALL Entity/DTO/VO fields):

/**
 * Account status: 0=disabled, 1=active (Must explain enum/dictionary values)
 */
private Integer accountStatus;

Inline Comments: Use // 1. Step description to divide complex logic blocks inside methods.

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🛠️ 3. Utility Classes & Anti-Reinvention

• Discovery First: NEVER reinvent the wheel. Always prefer established libraries (cn.hutool.*, org.apache.commons.*) or existing project utilities (*Util, *Helper).
• Strict Boundaries: Custom utility classes MUST be stateless: public final class with a private default constructor. All methods MUST be static.
• Acyclic Dependencies: Utility classes MUST NOT import business-level components (e.g., UserService or Entities).

---

🚀 4. Functional Programming & High-Performance Patterns

When writing complex data processing logic, you MUST use functional programming paradigms (Function, Consumer, BiConsumer) to abstract control flows.

Pattern A: In-Memory Data Assembly (Anti-JOIN)

Avoid nested for-loops when assembling cross-domain data. Parameterize the behavior:

public static <T, K, V> void assembleData(
        List<T> source,
        Function<T, K> keyExtractor,
        Function<List<K>, Map<K, V>> valueLoader,
        BiConsumer<T, V> resultSetter) {
    // 1. Extract Keys -> 2. Load Values in Batch -> 3. Iterate and Set
}

Pattern B: High-Volume Cursor Batching (Anti-LIMIT/OFFSET)

STRICTLY PROHIBITED to load massive datasets into memory at once or use deep pagination (LIMIT offset, size). MUST use Cursor/IDX-based batch processing:

public static <T, C extends Comparable<C>> void processInBatches(
        C initialCursor,
        int batchSize,
        BiFunction<C, Integer, List<T>> fetcher, // Query: WHERE id > cursor ORDER BY id ASC LIMIT batchSize
        Function<T, C> cursorExtractor,          // Extract cursor from the last element
        Consumer<List<T>> batchConsumer          // Consume the batch
) {
    C currentCursor = initialCursor;
    while (true) {
        List<T> batch = fetcher.apply(currentCursor, batchSize);
        if (batch == null || batch.isEmpty()) break;
        batchConsumer.accept(batch);
        currentCursor = cursorExtractor.apply(batch.get(batch.size() - 1));
    }
}