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Learn Java

A free, interactive online Java course. You write Java on every lesson, with AI hints when something doesn't compile, and a free certificate when you finish.

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View syllabusJava playground

233,880+ codders enrolled

219 lessons198 challenges1,464 quiz questions

  • Beginner friendly
  • sparkles iconAI-assisted coding help
  • hint iconHands-on interactive lessons
  • volume On iconAudio narration on every lesson
  • quiz iconQuizzes to test your knowledge
  • certificate iconFree certificate of completion

Syllabus

3 sections3 projects219 lessons198 challenges1,464 quiz questions
  1. Section 1

    Fundamentals

    Start sectionStartExpandCollapse    Build a strong foundation with essential concepts and basic skills73 lessons96 challenges445 questions1 project

    Introduction

    4 lessons424

    Variables Part 1

    5 lessons940

    Variables Part 2

    5 lessons333

    Operators Part 1

    7 lessons956

    Operators Part 2

    5 lessons834

    Decision Making

    6 lessons1038

    Basic IO

    5 lessons723

    Calculator App

    Project4 lessons1

    Loops

    9 lessons1362

    Methods (Functions)

    7 lessons843

    Arrays Basics

    6 lessons929

    Iterating Over Arrays

    3 lessons423

    String Operations

    4 lessons832

    Final Challenges

    3 lessons38
  2. Section 2

    Logic & Flow

    Start sectionStartExpandCollapse    Master advanced Java programming with a focus on data structures and flow control. Learn to work with complex arrays, collections, error handling, and time management.59 lessons82 challenges387 questions1 project

    Multi-dimensional Arrays

    9 lessons1457

    HashMap Part 1

    6 lessons637

    HashMap Part 2

    6 lessons1030

    HashSet Part 1

    7 lessons844

    HashSet Part 2

    6 lessons1146

    Advanced Control Flow

    5 lessons929

    Basic Error Handling

    4 lessons630

    Advanced String Operations

    6 lessons1145

    Project - Unique Word Counter

    Project4 lessons123

    Date and Time

    6 lessons646
  3. Section 3

    Object Oriented Programming

    Start sectionStartExpandCollapse    Discover how to organize code with classes, objects, and reusable structures87 lessons81 challenges632 questions1 project

    Fundamentals of OOP

    9 lessons971

    Access Modifiers & Encapsulate

    5 lessons536

    Class Props & Static Member

    5 lessons533

    Inheritance

    8 lessons862

    Polymorphism

    6 lessons645

    Interfaces & Abstract Classes

    7 lessons754

    Special Methods & Object Class

    6 lessons644

    Advanced OOP Concepts

    6 lessons653

    Generics

    6 lessons644

    Exception Handling in OOP

    5 lessons536

    Design Patterns Part 1

    6 lessons654

    Design Patterns Part 2

    7 lessons763

    Project: Library Management

    Project7 lessons1

    Final Challenges

    4 lessons437

Java courses

Hands-on Java courses, free to start in your browser.

Interview PreparationData StructuresGraph Algorithms Courses

Beginner Challenges - Practice Basic Concepts

Popular

Put your beginner coding knowledge to test and try to solve this programming challenges, use any language you want, Happy Coding!

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Certificate on completion

  • 20
  • 20

Coding Problems

Popular

Put your programming problem solving skills to the test using the exercises with different difficulties in this course. Designed for coders with some prior knowledge of the basic syntax in any programming language.

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Certificate on completion

  • 32
  • 31

Stack - Data Structures Series #1

In this course, you will learn about the Stack data structure, create a Stack from zero using your preferred language, and practice coding challenges with it!

Data Structures
  • 13
  • 6
  • 1

Coding Problems: Volume 2

Put your programming problem solving skills to the test using the exercises with different difficulties in this course. Designed for coders with some prior knowledge of the basic syntax in any programming language. This course is an extension of the first Coding Problems

certificate icon

Certificate on completion

  • 25
  • 24

Hash Tables - Data Structures Series #4

In this course, you will learn about the Hash Table data structure, create a Hash Table from zero using your preferred language, and practice coding challenges with it!

Data Structures
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Certificate on completion

  • 14
  • 12

Linked List - Data Structures Series #5

In this course, you will learn about the Linked List data structure, create a Linked List from zero using your preferred language, and practice coding challenges with it!

Data Structures
certificate icon

Certificate on completion

  • 14
  • 6
  • 1
See all 47 Java courses →
What you get
Everything you'll use to learn to code

Learn by Doing

Write real code, query databases, build websites, and master AI prompts. Our interactive lessons cover every skill modern developers need.

playground.js
Code Editor
1const greeting = "Hello, Coddy!"
2function sayHi(name) {
3    return greeting + " " + name
4}
5
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Test #1test Case Success icon
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Test #3test Case Failure icon
Input
"Alex"
Output
"Hello, Coddy! Alex"

Build Your Coding Streak

Stay consistent and watch your progress grow! Track your daily coding habit, protect your streak with freeze days, and earn rewards for showing up every day.

12 days streak

Return tomorrow to keep your streak!

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January 2026

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Double or Nothing

Day 5 of 7

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Streak Freeze

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Code Anywhere, Anytime

Take your coding journey on the go! No setup, no downloads - just open and start coding. Available on iOS, Android and Web with 4.9 star ratings.

Python
7Streak
250Score
5Energy
Variables
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CONTINUE
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Journey
Goals
Leaderboard
Profile
4.9
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Rating

You're Not Alone in This

Compete on global leaderboards, invite friends to earn rewards, and celebrate each other's wins. Coding is better with friends!

Challenger League
Challenger LeagueTop 7 advance
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Alex7+ Days
2840
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Jordan7+ Days
2650
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Sam7+ Days
2420
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Casey
2180
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Morgan7+ Days
1950
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Every way to learn

Read, listen, test yourself, ask the AI, or look up anything you've already covered. Every lesson meets you where you are.

Intro to Variables
Audio

A variable is a named container that stores a value you can reference later in your program.

In Python, you create one by writing the name, an equals sign, then the value you want to store.

The value can change over time - reassigning the name simply points it to a new value.

1xSarah

Prove Your Skills

Earn certificates for every course you complete. Add them to your LinkedIn profile and resume to showcase your coding expertise to employers.

CoddyCertificate of Completion
This certifies thatJohn Doehas successfully completed
PythonPython Fundamentals
Verified
DateJan 2026
LinkedInAdd to LinkedIn

Why learn Java with Coddy

  • Write and run real Java code in your browser. No JDK install, no IDE setup. The editor compiles and runs your Java program server-side and shows the output instantly.
  • Object-oriented Java the way it's used in the real world: classes, inheritance, interfaces, polymorphism, generics, exception handling. Every concept gets a hands-on exercise.
  • AI hints help you read and fix Java errors, especially the verbose stack traces, so the language feels less intimidating from day one.
  • Free Java certificate when you finish the course. A credible signal for backend, Android, or enterprise roles where Java fluency matters.

Frequently asked questions about learning Java

Is Java hard to learn?

Java is more verbose than scripting languages like Python or JavaScript. Every program needs a class, methods are declared with explicit types, and you compile before you run. The upside is that the strictness teaches good habits early. The course explains why each piece exists, which makes the verbosity feel less arbitrary.

How long does it take to learn Java?

Java basics - syntax, methods, classes, objects - take two to four weeks of daily practice. Comfortable use of inheritance, interfaces, and the standard collections takes one to three months. Going deeper into Spring, Android, or backend work is a separate ramp on top of that.

Should I learn Java or Python first?

Pick based on goal, not difficulty. Python is shorter to write and great for data, scripting, and AI. Java is the standard for Android, enterprise backends, and large team codebases - and the strict typing teaches OOP fundamentals that transfer everywhere. With no specific target, Python is faster to feel productive in.

Can I learn Java for free online?

Yes. The interactive Java course is free - lessons, coding exercises, quizzes, and a certificate of completion. The editor runs in the browser so you don't need to install the JDK locally to start coding Java.

Do I need to install Java to use this course?

No. Every Java exercise compiles and runs server-side in a sandboxed environment, and the output shows up next to your code. No JDK, no IDE, no project setup.

Do I get a Java certificate at the end?

Yes. Finishing the Java course gives you a free certificate of completion. Not a university accreditation, but a verifiable signal that you've worked through a structured, interactive Java course with real coding exercises.
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Learn Java with Coddy

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