Java Interview Questions & Answers — My Prep Notes

These are my personal prep notes for technical interviews as a final-year engineering student. Not exhaustive — a working set I keep updating as I study. Corrections welcome.

OOP Fundamentals

Collections

Exceptions

Multithreading & Concurrency

JVM Internals

Quick-fire round

A few I drill with flashcards before interviews:

== vs .equals() — == compares references (or primitive values); .equals() compares logical equality, as defined by the class.
String pool — string literals are interned; new String("x") forces heap allocation outside the pool.
Why are Strings immutable? — thread safety, safe hashcode caching (used heavily as HashMap keys), and security (can't be mutated after being passed to sensitive APIs like file paths or class loaders).
final vs finally vs finalize() — final = constant/no override/no subclass (context-dependent); finally = guaranteed cleanup block; finalize() = deprecated GC hook, don't use it.

I'll keep updating this as I go through more prep — if you're studying for the same kind of interviews, treat this as a living checklist, not a finished reference.

These are my personal prep notes for technical interviews as a final-year engineering student. Not exhaustive — a working set I keep updating as I study. Corrections welcome.

== vs .equals() — == compares references (or primitive values); .equals() compares logical equality, as defined by the class.
String pool — string literals are interned; new String("x") forces heap allocation outside the pool.
Why are Strings immutable? — thread safety, safe hashcode caching (used heavily as HashMap keys), and security (can't be mutated after being passed to sensitive APIs like file paths or class loaders).
final vs finally vs finalize() — final = constant/no override/no subclass (context-dependent); finally = guaranteed cleanup block; finalize() = deprecated GC hook, don't use it.

I'll keep updating this as I go through more prep — if you're studying for the same kind of interviews, treat this as a living checklist, not a finished reference.

Java Interview Questions & Answers — My Prep Notes

OOP Fundamentals

Collections

Exceptions

Multithreading & Concurrency

JVM Internals

Quick-fire round

On this page

Java Interview Questions & Answers — My Prep Notes

OOP Fundamentals

Collections

Exceptions

Multithreading & Concurrency

JVM Internals

Quick-fire round

On this page

Java Interview Questions & Answers — My Prep Notes

What's the difference between an abstract class and an interface?

Explain polymorphism with a concrete example.

What is the difference between method overloading and overriding?

Why is Java not 100% object-oriented?

ArrayList vs LinkedList — when would you use each?

HashMap vs TreeMap vs LinkedHashMap?

How does HashMap handle collisions?

What's the difference between Comparable and Comparator?

Checked vs unchecked exceptions?

What happens if you throw an exception inside a finally block?

What is try-with-resources and why does it matter?

What's the difference between synchronized and a Lock (java.util.concurrent.locks)?

What is a race condition, and how do you prevent it?

Explain the volatile keyword.

What's the difference between the stack and the heap?

How does garbage collection work, at a high level?

What causes a memory leak in Java, given it has a garbage collector?

On this page

Java Interview Questions & Answers — My Prep Notes

What's the difference between an abstract class and an interface?

Explain polymorphism with a concrete example.

What is the difference between method overloading and overriding?

Why is Java not 100% object-oriented?

ArrayList vs LinkedList — when would you use each?

HashMap vs TreeMap vs LinkedHashMap?

How does HashMap handle collisions?

What's the difference between Comparable and Comparator?

Checked vs unchecked exceptions?

What happens if you throw an exception inside a finally block?

What is try-with-resources and why does it matter?

What's the difference between synchronized and a Lock (java.util.concurrent.locks)?

What is a race condition, and how do you prevent it?

Explain the volatile keyword.

What's the difference between the stack and the heap?

How does garbage collection work, at a high level?

What causes a memory leak in Java, given it has a garbage collector?

On this page