java-expert

name	java-expert
description	Optimize and fix Java source code while preserving all functional interfaces, variables, classes, and method signatures
category	code
version	1.0.0
author	DocSys Team
permissions	["read","write"]
tags	["java","code","optimize","fix","refactor","compile"]

Java Expert

Analyze, optimize, and fix Java source code. Preserve ALL functional interfaces, variable names, class names, method signatures, and API contracts — only improve implementation quality, correctness, and performance.

Triggers

优化 java, 修复 java, java 代码, java 错误, java 问题, 编译错误, fix java, optimize java, java compile error, java bug, java 代码优化, java 重构, java refactor, java performance, java 性能, java 语法错误, java syntax error, java exception, java 异常, java class, java 方法, java 脚本

Workflow

1. Read the source code — Read all Java files fully, do not summarize or skip content
2. Identify the problem — compilation error, runtime exception, logic bug, performance issue, or style problem
3. Check unchanged contracts — Confirm all public/protected method signatures, class names, field names, and interface implementations are preserved
4. Apply fix — Minimal, focused change that fixes the root cause without altering the API surface
5. Verify compilation — If build tool available, verify mvn compile or javac passes with no errors

Golden Rules

• NEVER change method signatures (name, parameters, return type, throws clauses)
• NEVER rename public/protected fields, variables, or class names
• NEVER remove existing interface implementations or superclass relationships
• DO change method body implementation, variable scope, algorithm, error handling
• DO add null checks, bounds checks, logging, and defensive guards
• DO fix logic errors, off-by-one bugs, resource leaks, concurrency issues
• DO improve performance (loops, data structures, caching) while preserving semantics

Common Fixes

Category	Symptom	Fix
Compilation error	syntax error, type mismatch	Correct syntax, add cast, fix generics
Null pointer	NPE on method call	Add null check guard, Objects.requireNonNull
Resource leak	stream/connection not closed	Use try-with-resources
Concurrency	race condition	Add synchronized, volatile, or concurrent collection
Logic bug	wrong output	Fix algorithm, correct condition, fix boundary
Performance	slow loop, O(n²)	Use better data structure, algorithm optimization
Missing brace	unclosed block	Close all blocks properly
Import error	package not found	Fix import path, use fully-qualified name

CLI Command (optional)

# Compile check
mvn compile -f /path/to/pom.xml

# Single file compile
javac -cp "lib/*" src/Main.java

# Run tests
mvn test -f /path/to/pom.xml

Parameters

Parameter	Required	Description
file_path	Yes	Absolute path to the Java file to fix
problem_type	No	"compile" / "runtime" / "logic" / "performance" / "style"
preserve_contracts	Yes	Must always be true — never change API surface

Examples

Example 1 (编译错误修复)

User: "Fix the compilation error in MainAgent.java" Problem: The switch statement at line 403 is missing a closing brace } Skill triggers → reads MainAgent.java → identifies brace mismatch Fix: Add missing } before line 670 Output: Fixed MainAgent.java:670 — added closing } for switch statement. Compilation passes.

Example 2 (空指针异常修复)

User: "java 代码有空指针异常" Problem: redisTemplate may be null but is used without null check Skill triggers → reads RedisSessionService.java → finds method using redisTemplate Fix: Add if (redisTemplate == null) { return; } guard at method start Output: Fixed RedisSessionService.java — added null guard for redisTemplate field.

Example 3 (逻辑错误修复)

User: "修复 list_docs 的逻辑，查询条件写错了" Problem: List docs pattern matching incorrectly excludes results Skill triggers → reads MainAgent.java → finds pattern: nluQuery.contains("里的") too broad Fix: Narrow pattern to nluQuery.contains("里的文件") or nluQuery.contains("目录") Output: Fixed MainAgent.java:586 — refined list_docs pattern matching logic.

Example 4 (性能优化)

User: "优化这个循环的性能" Problem: Nested loop O(n²) when looking up by key Skill triggers → reads code → identifies HashMap lookup could replace loop Fix: Use Map.get(key) instead of iterating all entries Output: Fixed — replaced O(n²) loop with O(1) HashMap lookup. Performance improved.

Example 5 (语法错误)

User: "Maven 编译报语法错误" Problem: Duplicate variable declaration in method scope Skill triggers → runs mvn compile → sees "variable already defined" error Fix: Rename inner variable or merge logic to use single variable Output: Fixed — removed duplicate variable declaration. Compilation passes.

Example 6 (并发安全)

User: "这个多线程代码有线程安全问题" Problem: Shared mutable state accessed without synchronization Skill triggers → reads code → finds counter/sum shared across threads Fix: Add synchronized keyword or use AtomicInteger / ConcurrentHashMap Output: Fixed — added thread-safe concurrent access pattern.

Output Format

Success (English):

[java-expert] Fixed <file_path>

Problem: <brief description of the issue>
Root Cause: <why it happened>
Fix Applied: <what was changed>
Verification: <mvn compile passes / no errors>

Before:
<code snippet before fix>

After:
<code snippet after fix>

Success (中文):

[java-expert] 已修复 <file_path>

问题: <问题简要描述>
根本原因: <为什么会发生>
修复内容: <具体修改了什么>
验证结果: <编译通过 / 无错误>

修复前:
<code snippet>

修复后:
<code snippet>

Field	English	中文
problem	"Compilation error"	"编译错误"
root_cause	"Missing closing brace"	"缺少闭合大括号"
fix_applied	"Added } at line 670"	"在第670行添加了}"
verification	"mvn compile passed"	"编译通过"

Error — File not found: "Java source file not found at . Please provide a valid absolute path." Error — No write permission: "Cannot modify file — no write permission. Check file ownership." Error — API contract violated: "⚠️ REFUSE: This fix would change a public method signature (<class.method>). Only implementation changes allowed."

Error Handling

Error	Cause	Recovery
File not found	Path doesn't exist	Ask user for correct absolute path
No write permission	OS permission denied	Suggest using sudo or checking file ownership
Build not available	No mvn/javac found	Verify fix manually by code inspection
API contract violation	Attempted to rename method/field	Reject fix, explain golden rule

See references/ for Java best practices, common patterns, and style guides.