// modern java, taught in depth — not memorized

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StreamsDemo.java

1// group orders by customer, keep the big spenders

2Map<String, Long> loyal =

3 orders.stream()

4 .filter(o -> o.total() > 100)

5 .collect(Collectors.groupingBy(

6 Order::customer, counting()));

8var top = loyal.entrySet().stream()

9 .max(Map.Entry.comparingByValue());

compiled & running

// why java handbook

Depth over shallow tutorials

I'm Gopi — a developer who wanted a Java resource that actually goes deep. Every course is broken into clear, structured lessons with enough depth to use in real projects and interviews, not just to pass a quiz.

Structured paths

From fundamentals to advanced systems, laid out as a route you can follow.

Concept + practice

Each lesson pairs the idea with real, runnable code you write yourself.

Interview-ready

Data structures and patterns framed the way they actually get asked.

Always growing

New lessons and courses added regularly, from Kafka to Flink.

// the learning path

A route from first line to production

Not sure where to start? Follow the path — each stage builds on the last.

01 · core

Fundamentals

Syntax, OOP, collections, the JVM.

02 · dsa

Data structures

Arrays, maps, trees — and the problems.

03 · modern

Functional & Streams

Lambdas, the Streams API, Maven.

04 · scale

Systems

Kafka, Flink, distributed design.

// featured courses

Start where you are

Hand-picked courses to begin with — pick a level and go deep.

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