Free Core Java Course

Core Java Tutorial

Learn Java step by step, from your first program to collections and multithreading. Every lesson has clear explanations, runnable examples with real output, and interview-style FAQs, for beginners and experienced developers alike.

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138 tutorials
23 learning tracks
96 practice programs
Beginner to advanced

What Is Java?

Java is a high-level, object-oriented, general-purpose programming language created by James Gosling at Sun Microsystems and released in 1995. Java programs are compiled into bytecode that runs on the Java Virtual Machine (JVM), so the same program runs on Windows, Linux and macOS: "write once, run anywhere". Today Java powers enterprise back ends, Android apps, big-data platforms, financial systems and cloud microservices.

ParadigmObject-oriented, with functional features

TypingStatic and strong

MemoryAutomatic garbage collection

Runs onThe JVM, on any platform

Read the full introduction to Java

What You Will Learn

How Java works: the JDK, JRE, JVM, bytecode and the JIT compiler
Core syntax: data types, variables, operators, control flow and arrays
Object-oriented programming: classes, inheritance, polymorphism, abstraction and interfaces
Robust code with exception handling and try-with-resources
Working with text using String, StringBuilder and related classes
The Collections Framework: lists, sets, maps and when to use each
Concurrency with threads, synchronization and thread pools
Modern Java features: lambdas, records, switch expressions, pattern matching and virtual threads
Problem solving through 96 practice programs and interview-style FAQs

Who this is for

Students and beginners learning their first programming language, developers coming from other languages, and Java developers refreshing fundamentals or preparing for interviews.

Prerequisites

No prior Java experience is needed. Basic computer skills help; some familiarity with any programming language makes the first steps faster.

How a Java Program Runs

Write the source code. Save your program in a .java file, such as HelloWorld.java.
Compile it. The javac compiler checks the code and turns it into platform-independent bytecode in a .class file.
Load and verify. The JVM's class loader loads the bytecode and the verifier checks it for safety.
Execute. The JVM interprets the bytecode and its JIT compiler turns frequently used code into fast native machine code.
Manage memory. The garbage collector automatically frees objects that are no longer used.

Learn the difference between JDK, JRE and JVM

Core Java Learning Path

Follow the 23 tracks in order, or jump straight to the topic you need. Each tutorial includes runnable examples with their output and 20 frequently asked questions.

Overview

What Java is, how it runs, setting up the JDK, and how it compares with other languages.

Basics

Classes, objects, data types, variables, methods and your first Java program.

Operators

Arithmetic, relational, logical, bitwise, assignment, unary and ternary operators.

Control Statements

Decisions and loops: if-else, switch, for, while, do-while, break and continue.

Array

Single, multidimensional, jagged and anonymous arrays.

Constructors

Creating objects: default, parameterised, copy and private constructors, and chaining.

Exception Handling

try-catch-finally, try-with-resources, throw vs throws and custom exceptions.

Keywords

this, super, final, static, strictfp, transient, native and volatile explained.

OOPs Concept

Object-oriented programming: encapsulation, abstraction and abstract classes.

Interface

Interfaces, default methods, functional, marker and nested interfaces.

Polymorphism

Compile-time and runtime polymorphism: overloading and overriding.

Inheritance

IS-A and HAS-A relationships: inheritance and aggregation.

Multithreading

Threads, life cycle, priorities, daemon threads, thread pools and synchronization.

Nested Classes

Member, local, static nested and anonymous inner classes.

Miscellaneous

Garbage collection, enums, generics, serialization, packages, varargs and more.

String Classes

String, StringBuffer, StringBuilder, StringTokenizer and StringJoiner.

Collection Framework

The architecture of the Collections Framework and the Collection interface.

List

List, ArrayList, LinkedList and Vector.

Set

HashSet, LinkedHashSet, TreeSet, SortedSet and NavigableSet.

Map

HashMap, LinkedHashMap, TreeMap, Hashtable and specialised maps.

Lang Package

Core java.lang classes: Object, wrapper classes and Math.

Util Package

Date, Calendar, Arrays, Scanner, Optional and BitSet.

Programs

96 solved programs and patterns to practise what you learn.

Popular Java Comparisons

Clear side-by-side comparisons of classes and concepts that are easy to confuse and often asked in interviews.

Why Learn Java?

High Demand

Java is one of the most widely used languages in enterprise software, with strong demand for Java developers worldwide.

Platform Independent

Bytecode runs on any operating system with a JVM, from servers and desktops to the cloud.

Reliable and Secure

Strong typing, exception handling and managed memory make large applications stable.

Fast and Scalable

The JIT compiler, modern garbage collectors and virtual threads give excellent performance at scale.

Huge Ecosystem

Spring Boot, Hibernate, Kafka, Android and thousands of libraries build on Java.

Constantly Evolving

A new release every six months and long-term support versions keep Java modern and stable.

Spring Boot Build production-ready REST APIs and applications on top of your Java skills. Microservices Design, build and run microservices with Spring Boot. System Design Scalability, caching, load balancing and the architecture behind large systems.

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