Java Interview Questions

Hello reader! The purpose of this article is to share some common java interview questions that I was asked in the past when going through job interviews with top financial firms. I hope that you'll find this useful.

• What is a class?

• What is an object?

• Object VS class

• Method overloading.

• Method overriding.

• Access modifiers (private, public, protected, default).

• The difference between method overloading and method overriding.

• Object-Oriented Programming: inheritance, polymorphism, abstraction and encapsulation.

• Aggregation and association.

• Dynamic binding (linked to abstraction).

• Static keyword.

• Final keyword.

• Strings: discuss why they're immutable and what happens in the memory (stack and heap). The string is a class.

• Stringbuilder VS Stringbuffer.

• Interface: why it's used.

• Can we have multiple inheritance? If not, why? What can we do instead?

• Difference between abstract class and interface.

• Memory management: garbage collection, the types of garbage collectors.

• How does a hashmap work internally?

• Collections Framework.

• Exception handling: throw, throws keywords, what is a runtime exception.

• Runtime Type Checking.

• Difference between the keywords final, finally, finalize.

• try...catch block.

• Finally block.

• Exception propagation.

• Multithreading: what is a thread, how to create a thread (Runnable interface OR Thread class).

• Thread safety.

• Synchronize.

• Difference between a set and a list.

• Java 11 features.

• JDK, JRE, JVM.

• SOLID Principles.

• Test-Driven Development.

• Git commands.

• What does "unboxing" mean?

• Is Java "pass-by-value" or "pass-by-reference"?

• How do you return multiple values in Java?

• What does "covariance" mean?

Related: Java Phone Interview Questions - Beginner Level

Good luck! 🍀🍀🍀