Java

Google Java Style Guide

Official Google Java coding standards for consistent, maintainable code.

Golden Rules

1. 2-space indentation — no tabs 2. Column limit: 100 characters 3. Use `@Override` whenever applicable 4. No wildcard imports — import specific types 5. Braces required even for single-statement blocks 6. One top-level class per file 7. Prefer interfaces for type definitions

Quick Reference

Naming Conventions

Classes

// ✓ CORRECT
public class Animal {
    private final String name;

    public Animal(String name) {
        this.name = name;
    }

    public String speak() {
        return name + " makes a sound.";
    }
}

Control Structures

// ✓ CORRECT - braces always required
if (condition) {
    doSomething();
}

// ✗ INCORRECT - no braces
if (condition)
    doSomething();

// ✓ CORRECT - enhanced for loop
for (String item : items) {
    process(item);
}

Exception Handling

// ✓ CORRECT
try {
    processData(input);
} catch (IOException e) {
    logger.error("IO error: {}", e.getMessage());
    throw new ServiceException("Failed", e);
}

// ✓ CORRECT - try-with-resources
try (InputStream in = new FileInputStream(file)) {
    return IOUtils.toByteArray(in);
}

// ✗ INCORRECT
try {
    ...
} catch (Exception e) {    // too broad
    e.printStackTrace();   // don't use printStackTrace
}

Lambdas and Streams

// ✓ CORRECT
List<String> names = users.stream()
    .filter(u -> u.isActive())
    .map(User::getName)
    .sorted()
    .collect(Collectors.toList());

// ✓ CORRECT - method references
users.forEach(System.out::println);

Javadoc

/**
 * Finds a user by their unique identifier.
 *
 * @param userId the user's unique ID
 * @return an Optional containing the user, or empty if not found
 */
public Optional<User> findUserById(long userId) { ... }

Imports

// ✓ CORRECT
import java.util.List;
import java.util.Optional;

// ✗ INCORRECT
import java.util.*;  // no wildcard imports

Common Mistakes

When to Use This Guide

• Writing new Java code
• Refactoring existing Java
• Code reviews
• Setting up Checkstyle rules
• Onboarding new team members

Install

npx skills add testdino-hq/google-styleguides-skills/java

Full Guide

See java.md for complete details, examples, and edge cases.

Google Java Style Guide

Source: https://google.github.io/styleguide/javaguide.html

Golden Rules

1. 2-space indentation — no tabs 2. Column limit: 100 characters 3. Use `@Override` whenever applicable 4. No wildcard imports — import specific types 5. Braces required even for single-statement blocks 6. One top-level class per file 7. Prefer interfaces for type definitions

---

1. File Structure

// CORRECT
package com.example.project;

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

public class UserService {
    // ...
}

---

2. Naming Conventions

---

3. Classes

// CORRECT
public class Animal {
    private final String name;

    public Animal(String name) {
        this.name = name;
    }

    public String speak() {
        return name + " makes a sound.";
    }
}

---

4. Control Structures

// CORRECT - braces always required
if (condition) {
    doSomething();
}

// INCORRECT - no braces
if (condition)
    doSomething();  // braces required

// CORRECT - enhanced for loop
for (String item : items) {
    process(item);
}

---

5. Exception Handling

// CORRECT
try {
    processData(input);
} catch (IOException e) {
    logger.error("IO error: {}", e.getMessage());
    throw new ServiceException("Failed", e);
}

// CORRECT - try-with-resources
try (InputStream in = new FileInputStream(file)) {
    return IOUtils.toByteArray(in);
}

// INCORRECT
try {
    ...
} catch (Exception e) {    // too broad
    e.printStackTrace();   // don't use printStackTrace
}

---

6. Lambdas and Streams

// CORRECT
List<String> names = users.stream()
    .filter(u -> u.isActive())
    .map(User::getName)
    .sorted()
    .collect(Collectors.toList());

// CORRECT - method references
users.forEach(System.out::println);

---

7. Javadoc

/**
 * Finds a user by their unique identifier.
 *
 * @param userId the user's unique ID
 * @return an Optional containing the user, or empty if not found
 */
public Optional<User> findUserById(long userId) { ... }

---

Common Mistakes