Interview questions and answers

Pick a topic. Each guide groups its questions by module, gives a short answer to every one and links to the lesson that teaches it.

Java

Core Java, OOP, collections, streams, threads and the JVM, from the lessons that teach them.

Java Basics
Syntax, data types, operators, control flow, methods, arrays and strings.
Questions and answers
Java OOP
Classes, inheritance, polymorphism, abstraction, interfaces and encapsulation.
Questions and answers
Java Collections
List, Set, Map, Queue, generics and how the main collections work inside.
Questions and answers
Streams and Modern Java
Lambdas, streams, Optional, records and the newer language features.
Questions and answers
Exceptions and File I/O
Checked and unchecked exceptions, try-with-resources, files and robust error handling.
Questions and answers
Multithreading and Concurrency
Threads, synchronization, locks, executors and concurrent collections.
Questions and answers
JVM Internals
Class loading, memory areas, garbage collection and performance basics.
Questions and answers
Data Structures and Algorithms
Arrays, linked lists, trees, graphs, sorting, searching and complexity.
Questions and answers
Java Interview Rounds
Questions from the interview-preparation section: core Java, OOP, collections, output prediction and backend rounds.
Questions and answers

Python

Python basics, OOP, collections, idiomatic Python, asyncio and internals.

Core CS and SQL

DBMS, operating systems, computer networks and SQL: the subjects every placement round covers.

Backend

Spring Boot, Spring Security, FastAPI, REST and HTTP, and system design.

Written guides

Longer articles with runnable code, for the questions interviewers ask most.

All guides

Java

Java Basics

Java OOP

Java Collections

Streams and Modern Java

Exceptions and File I/O

Multithreading and Concurrency

JVM Internals

Data Structures and Algorithms

Java Interview Rounds

Python

Python Basics

Python OOP

Python Collections

Idiomatic Python

Concurrency and AsyncIO

Python Internals

Data Structures and Algorithms

Python Interview Rounds

Core CS and SQL

DBMS

Operating Systems

Computer Networks

SQL

Backend

Spring Boot

Spring Data JPA and Hibernate

Spring Security

FastAPI

REST and HTTP

System Design

Written guides

Java

Java Basics

Java OOP

Java Collections

Streams and Modern Java

Exceptions and File I/O

Multithreading and Concurrency

JVM Internals

Data Structures and Algorithms

Java Interview Rounds

Python

Python Basics

Python OOP

Python Collections

Idiomatic Python

Concurrency and AsyncIO

Python Internals

Data Structures and Algorithms

Python Interview Rounds

Core CS and SQL

DBMS

Operating Systems

Computer Networks

SQL

Backend

Spring Boot

Spring Data JPA and Hibernate

Spring Security

FastAPI

REST and HTTP

System Design

Written guides