About the online Java compiler
This page compiles and runs Java from your browser. Write a class with a main method, press Run, and the program output appears in the console. Compilation errors are shown with their line numbers.
You do not need to install a JDK or set up an IDE, so it is a convenient place to practise syntax, test a small class, or follow along with a Java lesson.
How to use it
- Write a class containing public static void main(String[] args).
- Press Run to compile and execute it.
- Read the output, or the compiler errors if the build fails.
- Edit and run again.
Example: sum the even numbers in a list
A short program that uses a stream to filter and add up values.
import java.util.List;
public class Main {
public static void main(String[] args) {
List<Integer> numbers = List.of(4, 7, 10, 13, 22);
// Keep the even numbers and add them up
int sum = numbers.stream()
.filter(n -> n % 2 == 0)
.mapToInt(Integer::intValue)
.sum();
System.out.println("Sum of even numbers: " + sum);
}
}What it is good for
- Practising Java syntax and object-oriented basics
- Testing collections, strings, and streams
- Checking the output of a snippet from a tutorial or textbook
- Preparing for coding interviews without opening an IDE
Frequently asked questions
Do I need to install the JDK?
No. Compilation and execution are handled for you, so a browser is all you need.
Why does my program say it cannot find the main method?
Java starts from a method with the exact signature public static void main(String[] args). Check the spelling, the modifiers, and that it sits inside your class.
Can I import classes from the standard library?
Yes. Standard packages such as java.util, java.time, and java.util.stream can be imported as usual.
Is the Java compiler free?
Yes. It is free and works without an account.