Whether you're preparing for your first Java developer role or aiming for a senior-level Java engineering position, being familiar with common Java interview questions can give you a strong advantage. Here’s a curated list of frequently asked Java interview questions along with concise and accurate answers.
✅ 1. What is Java?
Answer:
Java is a high-level, class-based, object-oriented programming language designed to have as few implementation dependencies as possible. It’s known for its platform independence, security features, and robust performance, making it a go-to language for enterprise and mobile applications.
✅ 2. What are the main features of Java?
Answer:
- Platform Independent: “Write once, run anywhere” using the Java Virtual Machine (JVM).
- Object-Oriented: Everything is treated as an object.
- Robust: Exception handling and memory management with garbage collection.
- Multithreaded: Java supports concurrent execution of threads.
- Secure: Bytecode verification and runtime security policies.
- High Performance: With JIT compiler and efficient memory management.
✅ 3. What is the difference between == and .equals() in Java?
Answer:
== compares object references (memory locations)..equals() compares object contents (actual values).
Example: "Hello" == "Hello" might be true due to string pool, but always prefer .equals() for content comparison.
✅ 4. What is the difference between ArrayList and LinkedList?
Answer:
FeatureArrayListLinkedListInternal StructureDynamic arrayDoubly linked listAccess TimeFast (O(1) for index)Slow (O(n))Insert/DeleteSlower (due to shifting)Faster (especially in middle)MemoryLess overheadMore overhead (due to pointers)
✅ 5. What is the Java Virtual Machine (JVM)?
Answer:
JVM is a part of the Java Runtime Environment (JRE) that executes compiled Java bytecode. It enables platform independence by translating bytecode into native machine instructions specific to the host OS and hardware.
✅ 6. What is multithreading in Java?
Answer:
Multithreading is the ability to run multiple threads (lightweight processes) concurrently. It improves performance in applications such as web servers or GUI apps.
- Threads can be created by extending
Thread or implementing Runnable. - Java also provides the
java.util.concurrent package for advanced concurrency.
✅ 7. What is the difference between final, finally, and finalize() in Java?
Answer:
final: A keyword used to declare constants or prevent overriding/inheritance.finally: A block used in exception handling to execute cleanup code.finalize(): A method invoked by the garbage collector before object destruction (deprecated in recent Java versions).
✅ 8. What is the difference between static and final in Java?
Answer:
static: Defines class-level members that are shared among all instances.final: Prevents changes — a final variable can't be reassigned, a final method can't be overridden, and a final class can't be extended.
✅ 9. What is the use of super and this keywords?
Answer:
this: Refers to the current class's instance.super: Refers to the parent class's members (fields/methods).
✅ 10. What are checked and unchecked exceptions?
Answer:
- Checked Exceptions: Checked at compile-time (e.g.,
IOException, SQLException). - Unchecked Exceptions: Runtime exceptions (e.g.,
NullPointerException, ArithmeticException).
🏁 Conclusion
These Java interview questions cover both fundamental concepts and advanced features used in real-world development. Mastering these topics can help you ace your technical interview and confidently explain core Java principles.