Java Best Practices for Clean Code
1️⃣ Write Clear, Intent-Revealing Names
Good names eliminate comments and confusion.
Do:
int retryCount;
List<User> activeUsers;
Don’t:
int x;
List<User> au;
Tips
Methods = verbs (calculateTotal())
Classes = nouns (OrderService)
Constants = all caps (MAX_RETRY)
2️⃣ Keep Methods Small and Focused
Each method should do one thing and do it well.
Good:
public double calculateDiscount(double price) { ... }
Bad:
public double processOrderAndSendEmailAndLog() { ... }
3️⃣ Avoid Long Parameter Lists
Prefer objects instead.
Refactor:
public void createUser(String name, String email, String password)
→ to:
public void createUser(User user)
4️⃣ Use Meaningful Exceptions
Don't just throw Exception.
Good:
throw new InvalidOrderException("Order ID is missing");
Tips
Don’t swallow exceptions silently.
Include context in exception messages.
Use custom exceptions sparingly but appropriately.
5️⃣ Favor Composition Over Inheritance
Inheritance can lead to tight coupling.
Prefer:
class EmailService {
private EmailClient client;
}
Avoid:
class EmailService extends EmailClient { ... }
6️⃣ Limit the Use of Static and Global State
Static = harder to test, harder to maintain.
Static OK for:
Utility methods
Constants
Not OK for:
Shared mutable data
Core business logic
7️⃣ Use Streams Carefully (Readable > Fancy)
Streams can be elegant, but don’t sacrifice clarity.
Readable:
users.stream()
.filter(User::isActive)
.collect(Collectors.toList());
Not readable:
users.stream().filter(u -> u.isActive()).map(u -> u.toString()).sorted().limit(3).collect(...);
8️⃣ Prefer Immutability
Immutable objects reduce bugs and side effects.
public record User(String name, String email) {}
Or:
class User {
private final String name;
}
9️⃣ Use Optional Properly
Use Optional as a return type—not for fields, not for parameters.
Good:
public Optional<User> findUserById(String id)
Avoid:
private Optional<User> user; // Not intended for fields
🔟 Write Unit Tests (and Make Them Fast & Independent)
Characteristics of good tests:
Deterministic
Small
Readable
One assertion per behavior
Framework examples:
JUnit 5
Mockito
AssertJ
11️⃣ Follow SOLID Principles
Single Responsibility
Open/Closed
Liskov Substitution
Interface Segregation
Dependency Inversion
These help keep your architecture clean and maintainable.
12️⃣ Use Clean Architecture Concepts
Keep domain logic pure
Separate infrastructure concerns
Use interfaces for abstractions
13️⃣ Favor Logging Over System.out
Use SLF4J/Logback.
private static final Logger logger = LoggerFactory.getLogger(MyClass.class);
logger.info("Order processed: {}", orderId);
14️⃣ Write Comments Only When Needed
Comment why, not what.
Bad:
i++; // increment i
Good:
// Using retry to avoid temporary API outage
15️⃣ Keep Code Consistent
Use:
Consistent formatting
Standard naming conventions
Consistent package structure
Recommended tools:
Checkstyle
Spotless
SonarLint
🧽 Summary: Clean Java Code Checklist
✔ Clear names
✔ Small, focused methods
✔ Logical class design
✔ Avoid duplication (DRY)
✔ Good exception handling
✔ Immutability where possible
✔ Minimize side effects
✔ Proper logging
✔ Meaningful tests
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