Effective Java: 15 Best Practices for Writing Clean and Efficient Code

Writing clean, efficient, and maintainable Java code is crucial for building scalable and high-performance applications. Whether you're developing enterprise software, microservices, or cloud-based applications, following Java best practices will help you avoid common pitfalls, reduce technical debt, and improve overall application performance.

In this guide, we will explore 15 essential best practices from Effective Java that every Java developer should follow to write robust, clean, and optimized code.

1️⃣ Use Java 21 and Stay Updated with the Latest Features

Why?

Java is constantly evolving, and newer versions introduce performance optimizations, security fixes, and better syntax improvements.

Best Practices

✔ Use Java 21 (LTS) for Virtual Threads, Pattern Matching, and Records.
✔ Upgrade dependencies to leverage new APIs and performance improvements.

Example: Using Virtual Threads in Java 21

ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
executor.submit(() -> System.out.println("Hello from Virtual Thread!"));

Benefit: Lightweight millions of threads without the overhead of traditional threads.

2️⃣ Use Records Instead of Boilerplate POJOs

Why?

Traditional POJOs (Plain Old Java Objects) require getters, setters, equals, hashCode, and toString, making the code verbose.

Best Practices

✔ Use records for data-carrying objects.
✔ Use regular classes when mutability is required.

Example: Using Records for Immutable Data Objects

public record User(String name, int age) {}

Benefit: Eliminates boilerplate code while keeping objects immutable.

3️⃣ Avoid Using Raw Types in Generics

Why?

Raw types can lead to type safety issues and runtime errors.

Best Practices

✔ Always use parameterized generic classes.
✔ Use bounded type parameters where necessary.

Example: Using Safe Generics

List<String> names = new ArrayList<>(); // ✅ Good
List rawList = new ArrayList();         // ❌ Bad (Raw Type)

Benefit: Ensures type safety and compile-time checks.

4️⃣ Prefer Streams and Functional Programming Over Loops

Why?

Traditional for-loops can be verbose and harder to read.

Best Practices

✔ Use Streams API for concise collection operations.
✔ Use lambda expressions to improve readability.

Example: Filtering Data with Streams

List<String> names = List.of("Alice", "Bob", "Anil");
List<String> filteredNames = names.stream()
    .filter(name -> name.startsWith("A"))
    .collect(Collectors.toList());

Benefit: Reduces boilerplate and improves readability.

5️⃣ Use Optional Instead of Null to Avoid NullPointerException

Why?

Returning null can lead to NullPointerExceptions (NPEs), making the code fragile.

Best Practices

✔ Use Optional<T> for better null handling.
✔ Avoid using Optional.get(), prefer orElse() or orElseThrow().

Example: Using Optional to Handle Null Values

public Optional<User> findUserByEmail(String email) {
    return Optional.ofNullable(userRepository.findByEmail(email));
}

Benefit: Avoids NullPointerExceptions and makes code more readable.

6️⃣ Use Static Factory Methods Instead of Constructors

Why?

Factory methods provide better readability and flexibility.

Best Practices

✔ Use static factory methods for object creation.
✔ Name them meaningfully (of(), from(), create()).

Example: Using Factory Methods

public static User create(String name, int age) {
    return new User(name, age);
}

Benefit: Improves code clarity and maintainability.

7️⃣ Favor Composition Over Inheritance

Why?

Inheritance creates tight coupling and leads to fragile class hierarchies.

Best Practices

✔ Prefer composition (Has-A relationship) over inheritance (Is-A relationship).
✔ Use interfaces instead of deep class hierarchies.

Example: Using Composition Instead of Inheritance

class Engine {
    void start() { System.out.println("Engine started"); }
}

class Car {
    private Engine engine = new Engine();
    void start() { engine.start(); }
}

Benefit: Improves flexibility and reusability.

8️⃣ Write Small, Single-Responsibility Methods

Why?

Long methods are hard to read, debug, and maintain.

Best Practices

✔ Keep methods short and focused.
✔ Follow the Single Responsibility Principle (SRP).

Example: Refactoring for Clean Code

class UserService {
    private final EmailService emailService;
    
    public void registerUser(User user) {
        validateUser(user);
        saveUser(user);
        emailService.sendWelcomeEmail(user);
    }
}

Benefit: Improves modularity and testability.

9️⃣ Use Lombok to Reduce Boilerplate Code

Why?

Writing getters, setters, constructors, and builders manually is tedious.

Best Practices

✔ Use Lombok annotations like @Data, @Builder, and @AllArgsConstructor.

Example: Using Lombok for POJOs

@Data
@AllArgsConstructor
public class User {
    private String name;
    private int age;
}

Benefit: Reduces clutter and improves code readability.

🔟 Avoid Blocking Calls in Asynchronous Code

Why?

Blocking I/O operations inside asynchronous workflows can degrade performance.

Best Practices

✔ Use CompletableFuture for async operations.
✔ Use Reactor’s Mono & Flux for reactive programming.

Example: Using CompletableFuture for Asynchronous Execution

CompletableFuture.supplyAsync(() -> fetchUserData())
    .thenApply(data -> process(data))
    .thenAccept(System.out::println);

Benefit: Enhances application responsiveness.

1️⃣1️⃣ Secure APIs with OAuth2 and JWT

Why?

Exposing APIs without security can lead to data breaches.

Best Practices

✔ Use OAuth2 & JWT for secure authentication.

Example: Secure REST API with OAuth2

@EnableWebSecurity
public class SecurityConfig extends SecurityFilterChain {
    protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests().anyRequest().authenticated()
            .and().oauth2ResourceServer().jwt();
    }
}

Benefit: Protects APIs from unauthorized access.

1️⃣2️⃣ Use SLF4J with Logback for Logging Instead of System.out.println()

Why?

Using System.out.println() for logging is inefficient, makes logs harder to manage, and lacks proper log levels.

Best Practices

✔ Use SLF4J with Logback for structured logging.
✔ Use log levels (INFO, DEBUG, ERROR, WARN) appropriately.
✔ Log meaningful messages and avoid logging sensitive data.

Example: Using SLF4J for Logging

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class UserService {
    private static final Logger logger = LoggerFactory.getLogger(UserService.class);

    public void createUser(User user) {
        logger.info("Creating user: {}", user.getName());
    }
}

Benefit: Improves performance, log management, and debugging.

1️⃣3️⃣ Use Database Connection Pooling for Efficient Resource Management

Why?

Creating new database connections for every request is expensive and slows down the application.

Best Practices

✔ Use HikariCP (Default in Spring Boot) for better performance.
✔ Set maximum pool size and connection timeout.

Example: Configuring HikariCP in Spring Boot

spring.datasource.hikari.maximum-pool-size=10
spring.datasource.hikari.minimum-idle=5
spring.datasource.hikari.connection-timeout=30000
spring.datasource.hikari.idle-timeout=60000

Benefit: Improves application performance and scalability.

1️⃣4️⃣ Always Close Resources Using Try-With-Resources

Why?

Failing to close database connections, file streams, and sockets can lead to memory leaks.

Best Practices

✔ Use try-with-resources for automatic resource management.
✔ Ensure all external resources are closed properly.

Example: Using Try-With-Resources to Close Resources

try (BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
} catch (IOException e) {
    e.printStackTrace();
}

Benefit: Prevents memory leaks and resource exhaustion.

1️⃣5️⃣ Write Unit Tests and Integration Tests to Ensure Code Quality

Why?

Not writing tests can lead to unexpected failures in production.

Best Practices

✔ Write JUnit tests for unit testing.
✔ Use Mockito for mocking dependencies.
✔ Use Testcontainers for integration testing.

Example: Writing a Unit Test for a Service Layer Using JUnit & Mockito

@ExtendWith(MockitoExtension.class)
class UserServiceTest {
    @Mock private UserRepository userRepository;
    @InjectMocks private UserService userService;

    @Test
    void shouldReturnUserById() {
        User user = new User(1L, "John Doe", "john@example.com");
        when(userRepository.findById(1L)).thenReturn(Optional.of(user));

        User result = userService.getUserById(1L);
        assertEquals("John Doe", result.getName());
    }
}

Benefit: Improves code reliability and maintainability.

🎯 Conclusion

Following these 15 Java best practices will help you write more efficient, readable, and secure applications in 2025.

By leveraging modern Java features, writing clean and maintainable code, avoiding common pitfalls, and ensuring proper security, you can significantly improve your Java applications. 🚀

What’s Next?

Apply these best practices in your Java projects.
Stay updated with Java 21 and future releases.
Write scalable, maintainable, and high-performance Java applications! 🎯

🔑 Keywords:

Java best practices, Java 21, Java clean code, Effective Java, Java performance tips, Java logging best practices, Java database optimization, Java security, Java unit testing, Java memory management.

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