10 Coding Practices Every Senior Java Developer Should Know (with Real-World Examples)

If you're writing Java in production, these best practices are non-negotiable. Whether you're mentoring juniors or scaling systems, these habits define senior-level engineering.

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1. ✅ Name Things Clearly

Bad:

public void d(User u) { ... }

Good:

public void deleteUser(User user) { ... }

Clear names reduce bugs and make code easier to debug and maintain.

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2. 🧱 Apply SOLID Principles

Example – Open/Closed Principle (OCP)

Instead of:

if (shape instanceof Circle) { ... }

Use:

interface Shape {
    double area();
}

Add new shapes without modifying existing logic. That’s real extensibility.

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3. 🚫 Avoid null – Use Optional

Optional<User> user = userRepo.findById(id);
user.ifPresent(u -> sendEmail(u.getEmail()));

Encourages defensive coding and avoids NullPointerException.

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4. 🧼 Keep Business Logic Out of Controllers

Anti-pattern:

@GetMapping("/register")
public void register(@RequestParam String name) {
    if (name.length() > 10) ...
}

Best Practice:
Move validation and logic into service classes. Keep controllers thin.

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5. 🔄 Prefer Composition Over Inheritance

Instead of:

class PremiumUser extends User { ... }

Use:

class PremiumUser {
    private User user;
    private LoyaltyProgram loyaltyProgram;
}

Composition = more flexibility, fewer surprises.

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6. 🔒 Secure at Method Level

Use annotations like:

@PreAuthorize("hasRole('ADMIN')")
public void deleteUser(Long id) { ... }

Never rely only on frontend enforcement or URL security.

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7. 🔍 Log Intelligently

Avoid:

System.out.println("Order placed");

Do:

log.info("Order placed for orderId={}, userId={}", orderId, userId);

Structured logging helps with observability and tracing.

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8. 🧪 Write Focused Tests

Bad:

@Test void testAll() { ... }

Good:
Write one assert per test scenario. Use JUnit 5, Mockito, and Testcontainers where applicable.

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9. 🧹 Validate Early, Validate Always

Use Bean Validation:

public class PaymentRequest {
    @NotNull
    private String accountId;

    @Min(1)
    private BigDecimal amount;
}

Combine with @Validated in service or controller layers.

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10. 🛑 Don't Optimize Before It's Needed

Don’t:

buildHyperCustomCacheThatNoOneAskedFor()

Do:
Profile first. Optimize second. Trust JFR, VisualVM, or YourKit.

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