How do I compile and run these Java programs?

Install a JDK, compile with javac Main.java, then run with java Main.

Which Java version are these examples compatible with?

Examples target Java 8+, including lambdas and streams.

Can I safely copy and modify the examples?

Yes. Copy, modify inputs, and observe outputs to reinforce concepts.

Do these programs work on all platforms?

Programs compile and run on Windows, macOS, and Linux with a standard JDK.

Java Basics Examples

Start with beginner-friendly Java—printing and basic syntax. These concise examples build confidence and show how Java compiles and runs simple programs.

Java Program to Calculate the Area of a Triangle

Program (Java)

Example & Expected Output

Uses the formula 1/2 * base * height.

25.0

Program Output

Java "Hello, World!" Program

Program (Java)

Example & Expected Output

Prints a greeting to the console using System.out.println.

Hello, World!

Program Output

Java Program to Add Two Numbers

Program (Java)

Example & Expected Output

Adds two integers and prints their sum.

Program Output

Java Program to Find the Square Root

Program (Java)

Example & Expected Output

Computes square root using Math.sqrt.

9.0

Program Output

Java Program to Swap Two Variables

Program (Java)

Example & Expected Output

Swaps variables using a temporary variable.

4 3

Program Output

Java Program to Solve a Quadratic Equation

Program (Java)

Example & Expected Output

Computes roots using the quadratic formula.

2.0 1.0

Program Output

Java Program to Convert Kilometers to Miles

Program (Java)

Example & Expected Output

Converts km to miles (1 km ≈ 0.621371 mi).

6.21371

Program Output

Java Program to Convert Celsius to Fahrenheit

Program (Java)

Example & Expected Output

Uses the formula (C*9/5)+32.

77.0

Program Output

Java Program to Check if a Number is Positive, Negative, or Zero

Program (Java)

Example & Expected Output

Checks the sign of a number using conditionals.

zero

Program Output

Java Program to Check if a Number is Odd or Even

Program (Java)

Example & Expected Output

Uses modulo % 2 to determine parity.

odd

Program Output

Java Program to Compute Factorial

Program (Java)

Example & Expected Output

Computes factorial using iterative loop.

Program Output

Java Program to Print Fibonacci Series

Program (Java)

Example & Expected Output

Prints first N Fibonacci numbers.

0 1 1 2 3 5 8

Program Output

Java Program to Check Prime Number

Program (Java)

Example & Expected Output

Determines if a number is prime.

true

Program Output

Java Program to Count Vowels in a String

Program (Java)

Example & Expected Output

Counts vowels using regex.

Program Output

Java Program to Reverse a String

Program (Java)

Example & Expected Output

Reverses a string using StringBuilder.

avaJ

Program Output

Frequently Asked Questions

Install a JDK (Java Development Kit), then compile with javac Main.java and run with java Main. On macOS, Linux, or Windows, use the official OpenJDK builds or your package manager.

The examples target modern Java (Java 8 and above). If you use older versions, most examples will still work, but features like lambdas and streams require Java 8+.

Yes. These examples are intended for learning. Copy the code, experiment with changes (e.g., different inputs), and observe the output to deepen your understanding of Java fundamentals.

Yes. Java is platform-independent. The examples compile and run on major platforms (Windows, macOS, Linux) with a standard JDK.

Learn Java the Practical Way

Java powers enterprise applications, Android development, and countless backend systems. Practicing small, focused programs builds fluency with syntax and core concepts such as data types, control flow, methods, classes, interfaces, exceptions, collections, and streams.

On this page, you will find clean, well-formatted examples that run across platforms. Each example includes a short description and expected output so you can quickly verify your understanding. Explore the topics via the sidebar and extend the code to experiment further.

Whether you are preparing for interviews, working through coursework, or refreshing fundamentals, these examples offer a practical path to mastering Java. Bookmark the page and return often to keep improving.

Java Programming Examples — Learn by Doing

This collection of Java examples covers fundamental to intermediate concepts with clean, runnable code. Each program is self-contained — copy it into any Java IDE, online compiler, or your local development environment and run it immediately. The examples progress from basic syntax through object-oriented programming, data structures, and algorithms.

Java remains one of the most popular programming languages worldwide, ranking consistently in the top 3 on TIOBE, Stack Overflow, and GitHub. It powers Android apps, enterprise backends (Spring Boot), big data (Hadoop), and financial systems. Practising with small, focused examples is the fastest way to build Java fluency.

Topics Covered in These Examples

Basics: Hello World, variables, data types, operators
Control Flow: if/else, switch, for, while, do-while
Methods: Parameters, return values, overloading, recursion
Arrays: Declaration, iteration, sorting, searching
Strings: Manipulation, StringBuilder, comparisons
Math: Factorial, Fibonacci, prime numbers, GCD

OOP: Classes, objects, constructors, inheritance
Interfaces: Abstraction, polymorphism, default methods
Exceptions: try/catch, custom exceptions, throws
Collections: ArrayList, HashMap, HashSet, iterators
Streams: filter, map, reduce, collect (Java 8+)
File I/O: Reading, writing, BufferedReader, Files API

How to Use These Examples

Browse by topic — use the sidebar to jump to a specific category (loops, arrays, OOP, etc.)
Read the description — each example includes a brief explanation of what the program does
Copy and run the code — paste into our Java Compiler or any local IDE
Check the expected output — compare your result with the listed output
Modify and experiment — change values, add features, or combine examples to deepen understanding

Why Practice with Small Programs?

Research on skill acquisition shows that deliberate practice — focused, repetitive work on specific concepts — produces faster learning than reading alone. Small Java programs isolate one concept at a time, making it easy to understand, modify, and remember. This is why coding interviews test with small problems: they reveal fundamental fluency that large project experience alone cannot demonstrate.

Each example on this page is designed to be completed in 2–5 minutes, making them perfect for daily practice sessions, interview preparation, or quick reference when you forget a specific syntax pattern.

Java Development Environment

Online (no install): Use our free Java Compiler to run any example instantly in your browser
Local IDE: IntelliJ IDEA (recommended), Eclipse, VS Code with Java Extension Pack
JDK: Install OpenJDK 17+ (LTS) for full compatibility with modern Java features
Build tools: Maven or Gradle for larger projects (not needed for these examples)

Frequently Asked Questions

What Java version do these examples use?

Most examples use Java 8+ features. Some advanced examples use Java 17 features like records and text blocks. All run on the current LTS (Java 17 or 21).

Can I use these for interview preparation?

Yes. The examples cover the most common interview topics: arrays, strings, recursion, OOP, collections, and basic algorithms. Practice modifying them to solve variations.

Why does every example use public class Main?

In Java, the class name must match the filename. Using Main makes examples portable across online compilers that expect this convention. In real projects, you would name classes descriptively.

Are these examples free to use?

Yes, completely free. Copy, modify, and use them in your projects, homework, or learning materials without attribution.

Who Uses This Page?

CS students practising for exams and assignments. Job seekers preparing for Java technical interviews. Self-taught developers building foundational Java skills. Teachers looking for clean, copyable code examples for lessons. Android developers refreshing core Java knowledge. Backend engineers transitioning from other languages to Java/Spring Boot.