Java for Beginners: Learn the Basics and Run Code Online
Java is one of the most widely deployed programming languages on Earth. It powers Android apps, enterprise backend systems, banking software, and large-scale web services. In this guide, you'll learn Java fundamentals and run every example in our free online Java compiler — no JDK installation required.
Why Learn Java?
| Reason | Detail |
|---|---|
| Industry demand | Java is consistently in the top 3 most in-demand languages for jobs |
| Android development | Most Android apps are written in Java or Kotlin |
| OOP foundation | Java enforces strong OOP principles — great for learning software design |
Your First Java Program
public class Main {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
Run this in the Online Java Compiler.
Key rules: every Java program lives inside a class, the entry point is always public static void main(String[] args), and statements end with a semicolon.
Variables and Data Types
public class Main {
public static void main(String[] args) {
int age = 22;
double salary = 45000.50;
boolean isEmployed = true;
String name = "David";
System.out.println(name + " is " + age + " years old.");
System.out.println("Employed: " + isEmployed);
}
}
Control Flow and Loops
public class Main {
public static void main(String[] args) {
int marks = 78;
if (marks >= 90) System.out.println("Distinction");
else if (marks >= 60) System.out.println("Pass");
else System.out.println("Fail");
int n = 7;
for (int i = 1; i <= 10; i++) {
System.out.println(n + " x " + i + " = " + (n * i));
}
}
}
Java Methods
public class Main {
static int factorial(int n) {
if (n <= 1) return 1;
return n * factorial(n - 1);
}
static boolean isPrime(int n) {
if (n < 2) return false;
for (int i = 2; i <= Math.sqrt(n); i++) {
if (n % i == 0) return false;
}
return true;
}
public static void main(String[] args) {
System.out.println("5! = " + factorial(5));
System.out.println("Is 17 prime? " + isPrime(17));
}
}
OOP: Your First Class
public class Main {
static class Person {
String name;
int age;
Person(String name, int age) {
this.name = name;
this.age = age;
}
void introduce() {
System.out.println("Hi, I'm " + name + " and I'm " + age + ".");
}
}
public static void main(String[] args) {
Person p1 = new Person("Alice", 30);
Person p2 = new Person("Bob", 25);
p1.introduce();
p2.introduce();
}
}
Frequently Asked Questions
Do I need to install Java (JDK)?
No. Our free online Java compiler runs JDK 21 in the cloud.
What should I name my main class?
Name your public class Main. Our compiler looks for main inside a class called Main.
Is Java or Python better for beginners?
Python has gentler syntax, but Java enforces strong OOP habits from day one. If you want to work in enterprise software or Android, Java is the better starting point.
What's the difference between Java and JavaScript?
They are completely different languages. Java is compiled and statically typed. JavaScript is a scripting language for browsers and Node.js. Try our JavaScript Compiler to see the difference.
Practice Now
Open the Free Online Java Compiler and work through each example above — no setup, instant compilation feedback.
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