Java Interview Questions for 3 Years Experience (2025 Edition)

Top Java Interview Questions for 3 Years Experience

After three years of working as a Java developer, you’re expected to have a solid understanding of core Java, OOP principles, exception handling, collections, and Java 8 features. In this guide, we’ll walk through the most searched Java interview questions tailored for this experience level in 2025.

🔹 1. What is the difference between ArrayList and LinkedList?

Best Practice: Use ArrayList for frequent get operations, LinkedList for add/remove.

🔹 2. Explain equals() vs == in Java.

• == compares object references.
• equals() compares values (when overridden).

String a = new String("Java");
String b = new String("Java");
System.out.println(a == b);      // false
System.out.println(a.equals(b)); // true

🔹 3. What are the four pillars of Object-Oriented Programming?

1. Encapsulation – Bundling data with methods.
2. Abstraction – Hiding internal details.
3. Inheritance – Reusing base class features.
4. Polymorphism – Multiple forms (overloading/overriding).

🔹 4. What is the use of final, finally, and finalize()?

• final: Constant or cannot be overridden.
• finally: Ensures code is executed after try-catch.
• finalize(): Called by GC before object removal (deprecated in Java 9+).

🔹 5. How does the Collection framework work?

Java Collections framework provides data structures like:

• List (ArrayList, LinkedList)
• Set (HashSet, LinkedHashSet)
• Map (HashMap, TreeMap)
• Utilities: Collections, Arrays

🔹 6. What is the difference between HashMap and Hashtable?

🔹 7. How does Java achieve platform independence?

Java uses the Java Virtual Machine (JVM) to run compiled .class files across platforms. This “write once, run anywhere” capability makes Java platform-independent.

🔹 8. What is the use of Java 8’s Stream API?

The Stream API processes data in a functional style.

List names = Arrays.asList("Tom", "Jerry");
names.stream().filter(n -> n.startsWith("T")).forEach(System.out::println);

Useful methods: map(), filter(), collect(), sorted()

🔹 9. What is the difference between throw and throws?

• throw: Used to explicitly throw an exception.
• throws: Declares exceptions in method signature.

void method() throws IOException {
    throw new IOException("Error occurred");
}

🔹 10. How is exception handling implemented in Java?

Using try, catch, finally, and custom exceptions.

try {
   // risky code
} catch (Exception e) {
   e.printStackTrace();
} finally {
   // cleanup
}

🔹 11. Explain method overloading vs method overriding.

🔹 12. What are Lambda Expressions?

Lambda expressions enable functional programming in Java 8. Learn more on Lambda Expression.

List list = Arrays.asList(1, 2, 3);
list.forEach(n -> System.out.println(n));

🔹 13. What is the difference between Abstract class and Interface?

🔹 14. What is the use of Optional in Java?

Optional helps avoid NullPointerException.

Optional name = Optional.ofNullable("Tom");
System.out.println(name.orElse("Default"));

🔹 15. What is Autoboxing and Unboxing?

• Autoboxing: Primitive to wrapper conversion.
• Unboxing: Wrapper to primitive.

Integer x = 5; // Autoboxing
int y = x;     // Unboxing

🔹 16. Explain the lifecycle of a Java thread.

1. New
2. Runnable
3. Running
4. Blocked/Waiting
5. Terminated

Use Thread, Runnable, and ExecutorService for threading.

🔹 17. What are common real-world scenarios asked in interviews?

Example: How would you handle 10,000 records from a DB efficiently?

• Use pagination with LIMIT and OFFSET.
• Use Stream and Collectors wisely.
• Avoid memory-heavy operations.

🔹 18. How to make a class immutable in Java?

final class Student {
    private final String name;
    public Student(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
}

🔹 19. How does Garbage Collection work in Java?

• Removes unreachable objects.
• Uses algorithms like Mark-Sweep, Generational GC, and G1 GC.
• Tools: jconsole, VisualVM, jstat, jmap

🔹 20. What is the use of static keyword?

• Static Variable: Shared among all objects.
• Static Method: Belongs to class.
• Static Block: Initializes static variables.

✅ Final Thoughts

With 3 years of experience, you are expected to write clean Java code, follow best practices, and understand performance optimization. This curated list of Java interview questions for 3 years experience will prepare you for technical rounds and help you stand out. Download Java.

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