Java Interview Questions for 5 Years Experience (2025 Edition)

Java Interview Questions for 5 Years Experience (2025 Edition)

If you’re preparing for a Java developer role with 5 years of experience, you’re expected to have more than just knowledge of core Java. You should understand Java 8+ features, multithreading, design patterns, memory management, and real-world problem-solving. This guide covers the most searched Java interview questions that recruiters commonly ask in 2025.

1. Explain the difference between HashMap, LinkedHashMap, and TreeMap.

2. How does Java handle memory management?

Answer:
Java uses:

• Heap memory: For objects.
• Stack memory: For method calls and local variables.
• Garbage Collection (GC): Removes unused objects automatically.
  You can monitor memory with tools like VisualVM, jconsole, or jstat.

3. What is the difference between wait(), sleep(), and join()?

• wait(): Releases lock, used for thread communication.
• sleep(): Pauses thread but doesn’t release lock.
• join(): Waits for another thread to finish.

Thread t = new Thread(() -> {});
t.start();
t.join(); // Waits for t to complete

4. What is a deadlock? How to prevent it?

Deadlock occurs when two or more threads wait for each other indefinitely, holding locks.

Prevention:

• Use a consistent locking order.
• Use tryLock() with timeout.
• Avoid nested locks when possible.

5. How are design patterns used in Java?

Common patterns:

• Singleton – One instance.
• Factory – Object creation logic.
• Strategy – Switch behaviors dynamically.
• Observer – Event handling system.
• Decorator – Add responsibilities dynamically.

public class Singleton {
    private static final Singleton INSTANCE = new Singleton();
    private Singleton() {}
    public static Singleton getInstance() {
        return INSTANCE;
    }
}

6. What’s the difference between Callable and Runnable?

7. How do you implement a thread-safe singleton?

Double-checked locking:

public class SafeSingleton {
    private static volatile SafeSingleton instance;
    private SafeSingleton() {}
    public static SafeSingleton getInstance() {
        if (instance == null) {
            synchronized (SafeSingleton.class) {
                if (instance == null) {
                    instance = new SafeSingleton();
                }
            }
        }
        return instance;
    }
}

8. What are Stream operations in Java 8?

• Intermediate: map(), filter(), sorted()
• Terminal: collect(), forEach(), count()

List<String> list = Arrays.asList("a", "b", "c");
list.stream().filter(s -> s.equals("b")).forEach(System.out::println);

Learn More on Stream APIs

9. Explain SOLID principles in Java.

• S – Single Responsibility
• O – Open/Closed
• L – Liskov Substitution
• I – Interface Segregation
• D – Dependency Inversion

These principles are vital for writing scalable, testable, and clean code in large projects.

10. What are functional interfaces and how are they useful?

A functional interface has one abstract method and is used in lambda expressions.

@FunctionalInterface
interface MyFunc {
    int operate(int a, int b);
}

11. What is Optional and when should you use it?

Optional helps avoid NullPointerException.

Optional<String> name = Optional.ofNullable(null);
System.out.println(name.orElse("Default"));

Use Optional in method returns where null might be expected.

12. How does garbage collection work in Java?

Java GC uses algorithms like:

• Mark and Sweep
• Generational GC
• G1 GC (Garbage First)

Use System.gc() only when necessary. JVM mostly handles it well.

13. How is exception handling used in real-world Java?

Handle exceptions gracefully, log important info, and avoid exposing stack traces to users.

try {
    // risky code
} catch (IOException e) {
    logger.error("IO failed", e);
} finally {
    // cleanup
}

14. Describe Java memory leaks and how to avoid them.

Even with GC, memory leaks happen due to:

• Static references
• Unclosed resources
• Listeners that aren’t removed

Tools: VisualVM, JProfiler

Best Practices:

• Use try-with-resources
• Clean up listeners

15. Common real-time scenario question

Q: How would you handle millions of records in a REST API?

Answer:

• Use pagination (Pageable)
• Use streaming API if needed
• Cache frequent queries
• Tune JVM memory

16. What are best practices for writing Java code with 5 years of experience?

• Follow SOLID and clean code principles
• Use var wisely (Java 10+)
• Leverage Streams for readability
• Use meaningful logging (SLF4J, Logback)
• Write unit tests (JUnit 5, Mockito)

17. Describe how you manage code quality in your projects.

Answer:

• Code Reviews using GitHub/GitLab
• Static Analysis: SonarQube
• Code Formatters: Checkstyle
• Continuous Integration: Jenkins, GitHub Actions

18. What are strong Java 8+ features to master at this level?

• Stream API
• Functional programming
• Optional
• Method references
• Collectors.groupingBy
• LocalDate/Time APIs

19. Describe how equals() and hashCode() are related.

Both are critical for hash-based collections like HashMap and HashSet.

@Override
public boolean equals(Object o) {
    // equality logic
}

@Override
public int hashCode() {
    // must match equals logic
}

20. What’s your approach to debugging and troubleshooting Java applications?

• Use IDE tools like breakpoints & watchpoints
• Read logs
• Use jstack, jmap, VisualVM
• Profiling tools for memory/cpu issues
• Ask “Why” recursively

Conclusion

By 5 years into your Java career, you should demonstrate a strong command over core and advanced concepts, write clean, maintainable code, and debug complex issues. These java interview questions for 5 years experience are designed to reflect that real-world readiness and go beyond textbook answers. Download Java

• How to Use Arrays in Java (with Code Examples for Beginners)
• Compilation in Java – How It Works with Execution Flow, Steps, and Example
• How to Use loops in Java: For, While, Do‑While Explained
• How to Use If Else Statement in Java (With Examples)
• How to Understand Object-Oriented Programming in Java Easily