132 hands-on lessons take you from your first line of code to Spring Boot and microservices. Learn at your own pace, practise with an AI mentor, and always know which Java version you’re using.
Learn the stack companies hire for
How it works
A clear path, lessons you can try as you read, and practice that feels like the real thing.
Choose a goal, from complete beginner to interview-ready, and get the lessons in the right order.
See learning paths →Short lessons with runnable code, old-versus-new comparisons, quizzes and an AI mentor for every question.
Open lesson 1 →Practise real interview questions, take scored mock interviews, and build projects in the courses.
Practise interviews →Watch Java evolve
Tap a version and see the code rewrite itself. Every lesson tells you which Java it needs, so what you learn matches the code you’ll meet at work.
Explore every Java versionJava 7: loops and an anonymous class just to sort a list.
Work through them in order or jump to what you need. Progress is saved in this browser.
How Java runs, variables and types, operators, decisions, loops and arrays, methods, input and output, numbers and recursion.
Classes, the four pillars, interfaces, records, sealed types and the Object contract.
String, StringBuilder, the string pool, text blocks, formatting and regular expressions.
try, catch and finally, checked vs unchecked exceptions, try-with-resources, custom exceptions and good error design.
Step by step: threads, Runnable and Callable, then race conditions and synchronization, then thread pools, Fork/Join, CompletableFuture, concurrent collections and virtual threads.
Every List, Set, Map and Queue with an interactive visual for each one, sorting with Comparable and Comparator, and generics.
A 13-part deep dive with an interactive lab: hashing, buckets, put and get, collisions, load factor, resizing, treeification and the traps.
The classic "X vs Y" questions side by side: lists, sets, maps, sorting, iterators and fail-fast behaviour.
Dates and times, files and I/O, serialization, reflection, networking and internationalisation.
How the JVM manages memory and garbage collection, and how classes are loaded.
The features that changed Java: lambdas and functional interfaces, the Stream API, collectors and Optional.
A guided tour of every language feature from Java 10 to 25, then pattern matching, modules and the HTTP client in depth.
Big-O, sorting and searching, linked lists, stacks and queues, trees and graphs, and dynamic programming.
Writing code other people can read, the SOLID principles, and the design patterns you'll meet in real projects.
Maven and Gradle, logging, JUnit and Mockito, debugging, annotations and reflection, and JSON with Jackson.
From raw JDBC to entity mapping, the persistence context, N+1 queries and transactions.
How Spring really works: the IoC container, dependency injection, scopes and lifecycle, Java configuration, AOP and proxies, events, and the MVC request flow, with interactive labs.
Auto-configuration, configuration and profiles, Spring Data JPA, REST APIs, security and testing.
From the filter chain to OAuth 2.0: authentication, password storage, authorization, JWT, OpenID Connect, CSRF and CORS, with labs that sign real tokens and hash real passwords.
Service boundaries, gateways and discovery, messaging, resilience, sagas and deployment.
Java 25 (LTS), released Sep 2025. All 132 lessons run as written on it.
Each path puts the right lessons in order for one goal, whatever your level.
Free account
Every lesson works without an account. A free account adds the things that keep you going.
Free learner account
Keep every lesson free, then sign in to unlock AI mentoring, interview practice, synced progress, your personal study plan and a full learner dashboard.
Version hub
Release dates, what changed, the Java each one needs, and an upgrade planner for each.
Try them right here. Every tile below works the same way it does inside the lessons.
The same topic re-explains itself for where you are. Here’s “How HashMap works inside”:
Imagine a row of 16 lockers. The key's hash tells you which locker to use. If two keys pick the same locker, they share it in a small chain.
Sign in to unlock interview flashcards, scored practice and your personal preparation progress.
Collections.sort(words, new Comparator<String>() {
@Override
public int compare(String a, String b) {
return Integer.compare(a.length(), b.length());
}
});90 finished features you gain, plus every removal to check first
Open the full plannerProject-based courses with free preview lectures. Pay once with UPI, cards or net banking.
A free quick start: install Java, write real programs, and understand what you wrote.
Design, build, secure, test and ship a real REST API with Spring Boot, PostgreSQL and Docker.
Find and fix the slow queries that an ORM makes easy to write.
Questions
Yes. All 132 lessons, the learning paths, the version guides and the interview questions are free, with no account needed. Paid courses are optional, project-based extras.
Yes. The “Java from zero” path starts with installing Java and writing your first program, then builds up one small step at a time.
Lessons are written for modern Java (Java 25 is the current long-term support release), and each one shows the version its code needs. Pick your JDK at the top of the page and lessons tell you if something won’t run on it.
It’s powered by Claude. It explains code, reviews it for bugs, decodes error messages, writes practice quizzes and runs mock interviews. It’s free with fair-use limits, and like any AI it can make mistakes.
Project-based lectures with video and written notes, free preview lectures, and access for as long as the course is offered. You pay once with UPI, cards or net banking through Razorpay.
Yes, within the refund window if you haven’t completed much of the course. See the refund policy for the details.
Not yet. For now, the best proof of your skills is the projects you build and the interviews you pass.
Passwords are stored as secure hashes, sign-in uses protected cookies, and payments are handled by Razorpay, so we never see your card or UPI details. Without an account your lesson progress stays in your browser; with one, it’s saved to your account so it follows you to any device.
Start with lesson 1. No account, no card, no setup beyond installing Java.