Java Learning Path

Learn Java: From Fundamentals to Interview-Ready Skills

A structured Java roadmap written by working engineers. Every tutorial pairs concepts with runnable code, the mistakes beginners actually make, and the interview questions each topic unlocks. Follow the clusters in order, or jump to the topic you need.

40 Tutorials
8 Topic Clusters
Beginner to Advanced
Free Learning

Java Roadmap

Follow the Path in Order

01

Basics 9 tutorials

Syntax, variables, operators, loops, arrays and strings — your foundation.

beginnerWhat is Java?A plain-English introduction to Java: what it is, how it runs, where companies use it, and how you can write your first program today.6 min read beginnerJDK vs JRE vs JVM: What's the Difference?The JDK contains the JRE, which contains the JVM. Here is what each layer actually does, with the compile-and-run flow every interviewer expects you to explain.6 min read beginnerJava Variables: Declaration, Types and ScopeLearn how Java variables are declared and initialized, the difference between local, instance and static variables, and how scope decides what your code can see.6 min read beginnerJava Data Types Explained with ExamplesMaster all 8 primitive types, understand reference types, and learn the casting rules that decide whether your Java code compiles, overflows or behaves.7 min read beginnerJava Operators: Arithmetic, Logical, Bitwise and MoreEvery Java operator category explained with runnable examples — from integer division surprises to short-circuit logic, i++ vs ++i, and bit shifting.7 min read beginnerJava Control Statements: if, switch and Decision MakingHow Java programs make decisions: if, if-else, the ternary operator, switch statements and modern switch expressions, with the pitfalls interviewers love to test.6 min read beginnerJava Loops: for, while, do-while and for-eachEvery Java loop explained with runnable code: for, while, do-while and for-each, when to use each one, and how break and continue change the flow.7 min read beginnerJava Arrays: Declaration, Iteration and Common OperationsA practical guide to Java arrays: how to declare and initialize them, iterate safely, work with 2D arrays, and use the Arrays utility class for real tasks.7 min read beginnerJava Strings: String Pool, Immutability and Key MethodsWhy Java strings are immutable, how the string pool saves memory, why == fails where equals() works, and when StringBuilder beats String — with runnable examples.6 min read

02

OOP 5 tutorials

The four pillars every interviewer starts with.

beginnerJava OOP Concepts: The Four Pillars ExplainedEncapsulation, inheritance, polymorphism and abstraction explained with one running example, so the four pillars become working knowledge instead of definitions.7 min read beginnerEncapsulation in Java: Why Getters and Setters MatterPrivate fields plus public methods is the syntax; controlled access is the point. Learn how encapsulation protects object state, enables validation, and leads to immutable classes.5 min read beginnerInheritance in Java with Real ExamplesUnderstand how the extends keyword, super, and method overriding work together, and learn when inheritance helps your design and when composition is the better call.6 min read beginnerPolymorphism in Java: Compile-Time vs RuntimeOne method name, many behaviors. Learn how overloading resolves at compile time, how overriding resolves at runtime, and why dynamic dispatch powers every real Java framework.5 min read beginnerAbstraction in Java: Abstract Classes and InterfacesAbstraction hides how and exposes what. Learn abstract classes, interfaces, default methods, and the decision rule for choosing between them in real designs and interviews.5 min read

03

Collections 11 tutorials

List, Set and Map deeply — including HashMap internals.

intermediateJava Collections Framework: The Complete MapOne mental map of the entire Collections Framework: the interface hierarchy, the workhorse implementations, complexity trade-offs, and the rules for picking the right one.6 min read intermediateList Interface in Java: ArrayList, LinkedList and VectorThe List interface defines ordered, index-based collections in Java. Learn its core methods and how ArrayList, LinkedList and Vector implement them differently.6 min read intermediateArrayList in Java: Internal Working and OperationsArrayList is Java's workhorse collection. See how the backing array grows, what each operation costs in Big-O terms, and the traps that show up in interviews.5 min read intermediateArrayList vs LinkedList: When to Use WhichArrayList and LinkedList both implement List but behave very differently under load. Compare their complexity, memory and real-world performance dimension by dimension.6 min read intermediateSet Interface in Java: HashSet, LinkedHashSet, TreeSetSets reject duplicates — but HashSet, LinkedHashSet and TreeSet differ in ordering, speed and null handling. Learn which one fits each job.5 min read intermediateHashSet in Java: How It Works and When to Use ItHashSet gives you O(1) duplicate-free storage — because there is a HashMap inside. Learn the mechanics, the equals/hashCode contract and the traps.6 min read intermediateMap Interface in Java: HashMap, TreeMap and MoreUnderstand the Map interface, its four main implementations, and how to pick between HashMap, LinkedHashMap, TreeMap and Hashtable with confidence.6 min read intermediateHashMap in Java: Operations, Iteration and Best PracticesA practical guide to HashMap in Java — every core operation, all the iteration patterns, and the best practices that keep production code fast and bug-free.5 min read advancedHow HashMap Works Internally in JavaThe complete internal story of Java's HashMap — hash computation, bucket indexing, collision handling, treeification at threshold 8, and the 0.75 load factor resize.9 min read intermediateHashMap vs Hashtable: Key DifferencesEvery difference between HashMap and Hashtable that matters — synchronization, nulls, iterators, performance — and why new code should use neither for concurrency.6 min read advancedHashMap vs ConcurrentHashMap: Thread Safety ExplainedWhat actually goes wrong when threads share a HashMap, how ConcurrentHashMap's fine-grained locking fixes it, and how to choose between them.7 min read

04

Exception Handling 2 tutorials

Write code that fails safely and predictably.

beginnerException Handling in Java: try, catch, finally, throwHow Java reacts when things go wrong at runtime, and how try, catch, finally, throw and throws let you handle failures without crashing the program.6 min read intermediateChecked vs Unchecked Exceptions in JavaThe compiler forces you to handle checked exceptions but ignores unchecked ones. Here is why the split exists and how to choose for your own exceptions.6 min read

05

Multithreading 4 tutorials

Threads, synchronization and the classic concurrency traps.

intermediateMultithreading in Java: Threads, Runnable and ExecutorsHow to run code on multiple threads in Java — from extending Thread, to Runnable lambdas, to the ExecutorService pools you will actually use at work.5 min read intermediateThread Lifecycle in Java: All 6 States ExplainedEvery Java thread moves through six states defined in Thread.State. Learn what triggers each transition and watch the states change in runnable code.5 min read advancedSynchronization in Java: synchronized, Locks and volatileWhy two threads corrupt a shared counter, and how synchronized, ReentrantLock, volatile and atomic classes each fix a different part of the problem.6 min read advancedDeadlock in Java: Causes, Detection and PreventionDeadlock freezes threads forever without throwing an exception. Learn the four conditions that cause it, how to detect it with jstack, and how to prevent it.6 min read

06

Java 8 5 tutorials

The functional style modern Java codebases are written in.

intermediateJava 8 Features: The Complete Practical GuideEvery Java 8 feature that still matters in interviews and real projects — lambdas, Streams, Optional, default methods and more — with runnable examples.6 min read intermediateLambda Expressions in Java: Syntax and Real Use CasesLearn every lambda syntax variation, the effectively-final rule, method references, and the real situations where lambdas make Java code shorter and clearer.6 min read intermediateFunctional Interfaces in Java: Predicate, Function, Consumer, SupplierThe four core functional interfaces power every stream operation. Learn Predicate, Function, Consumer and Supplier with runnable examples and composition.6 min read intermediateJava Streams: filter, map, collect and BeyondFrom your first filter-map-collect pipeline to groupingBy, reduce and parallel streams — a practical, interview-focused guide to the Java Stream API.5 min read intermediateJava Optional: Stop Writing Null Checks the Wrong WayOptional was designed to make missing values explicit, not to replace every null check. Learn the API that matters and the anti-patterns to avoid.6 min read

07

JVM & Memory 3 tutorials

What actually happens when your code runs.

advancedJVM Architecture: Class Loader, Runtime Areas and Execution EngineFollow a .class file through the JVM: how the class loader subsystem, runtime data areas and the JIT-powered execution engine turn bytecode into running machine code.6 min read advancedJava Memory Management: Heap, Stack and MetaspaceWhere do your objects, local variables and class metadata actually live? A practical map of JVM memory with runnable examples and the flags that control each region.7 min read advancedJava Garbage Collection: How GC Really WorksGC roots, the generational hypothesis, and how G1 and ZGC actually reclaim memory — with runnable demos and the tuning flags that matter in production.7 min read

08

Modern Java 1 tutorials

Records, sealed classes and pattern matching.

intermediateJava 17 Features: Records, Sealed Classes and Pattern MatchingEverything you gain moving from Java 8 or 11 to 17: records, sealed classes, pattern matching, switch expressions and text blocks — with runnable examples.6 min read

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