02 — Learning Path (Runnable Code Order)

Part of: docs/00-INDEX.md · Tutorials: 02-learn/00-INDEX.md

Follow the numbers. Run each file with java <package>/<class>.java.

Prerequisite: Complete 03 Environment Setup (JDK, project on disk, IDE optional) before running code.

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Step 0 — Orientation

1. 03 Environment Setup — install JDK, download project, IDE, first run
2. 01 Tutorial & History
3. 02-learn/01 Getting Started
4. pkg0intro/intro1AboutJava → intro2HistoryOfJava → intro3Objectives

Level 1 — Beginner (`pkg1core` 1–14, 24–25)

core1HelloWorld → core2Variables → core3DataTypes → core4Operators → core5ControlStatements → core6Loops → core7Methods → core8ArraysDemo → core9StringsDemo → core24UserInput → core25ClassesAndObjectsDemo → core10Encapsulation → core11Inheritance → core12Polymorphism → core13AbstractionDemo → core14InterfacesDemo

Docs: 02-learn/02 – 02-learn/13

Level 2 — Intermediate (`pkg1core` 15–28, `pkg2versions`)

core15EnumsDemo → core16RecordsDemo → core17SealedClassesDemo → core18ExceptionsDemo → core19CollectionsDemo → core20GenericsDemo → core21FunctionalProgramming → core22StreamsDemo → core23OptionalDemo → core26ConstructorsDemo → core27StaticMembersDemo → core28ComparatorDemo → pkg2versions/versions1Java5Features → versions6Java21Features

Docs: 02-learn/14 – 02-learn/21

Level 3 — Senior (`pkg3`–`pkg6`)

• pkg3datastructures/datastructures0DynamicArray → …12UnionFind
• pkg4algorithms/algorithms1SortingAlgorithms → …7DivideAndConquer
• LeetCode: leetcode1 → leetcode12; then blind75/, official75/, interview150/, top100/ — see 04-reference/14-LeetCode.md
• pkg6jvm/jvm1ClassLoadingDemo → jvm3GarbageCollectionDemo

Docs: 02-learn/22 – 02-learn/25

Level 4 — Tech Lead (`pkg7`, `pkg8`)

• pkg7concurrency/concurrency1ThreadBasics → concurrency8LocksAndCoordination
• pkg8patterns/patterns1SingletonPattern → patterns23VisitorPattern
• 03-interview/18-SystemDesign.md
• 04-reference/02-JVMInternals.md

Docs: 02-learn/26 – 02-learn/27

Level 5 — Applied Java (`pkg9`–`pkg13`)

Topic	Package	Reference
File I/O	pkg9io	04-reference/04-IO.md
Networking	pkg10networking	04-reference/05-Networking.md
JDBC	pkg11jdbc	04-reference/06-JDBC.md
REST	pkg12restapi	04-reference/07-RestApis.md
Std libs	pkg13libs	04-reference/08-Libraries.md

Docs: 02-learn/28 – 02-learn/32

Level 6 — Ecosystem (`pkg14`–`pkg20`, `build/`)

Topic	Reference
Testing	04-reference/09-Testing.md
Modules	04-reference/10-Modules.md
Memory model	04-reference/11-MemoryModel.md
Serialization	04-reference/12-Serialization.md
Build	04-reference/13-BuildTools.md

Docs: 02-learn/33 – 02-learn/37

Interview-season daily routine

• 2 problems from pkg5leetcode
• 20 Q&A from 03-interview/00-INDEX.md
• 1 pattern from pkg8patterns re-implemented
• 1 JVM or concurrency topic reviewed