Why Use an Online Java Compiler?
Installing a JDK, setting JAVA_HOME, and creating a project is slow when you only need to test main(). An online Java compiler compiles and runs a class in the browser so students and interview candidates can check a snippet immediately.
Hemiley opens with public class Main and System.out.println("Hello, World!"). That matches textbooks and Programiz-style examples. You can keep public class Main — the sandbox is set up for it.
How Hemiley Compiles Java
Press Run and the snippet is compiled with JDK 21, then executed. System.out prints to the right-hand Output panel. javac errors (missing braces, wrong types) show before any run output.
Prefer public class Main. If you use another public class name, the sandbox still compiles it. Scanner input is optional: open Input and type lines before Run. Code is not saved as a Hemiley project.
Key Benefits
No JDK install
Compile Java in the browser when you cannot install Temurin, Oracle JDK, or IntelliJ.
public class Main
The starter matches standard Java teaching examples.
Compile then run
javac errors appear clearly; a clean compile prints Hello World.
Scanner / stdin
Optional Input panel for Scanner and System.in.
JDK 21
Modern Java language level for student and snippet work.
Free, no account
Compile as many short programs as you need without signing in.
Who Uses This Java Compiler?
CS students
Labs that require a Main class and console output.
Beginners
First System.out.println without installing an IDE.
Interview prep
Small algorithms with a main() driver.
Teachers
Live-compile a demo class on a projector.
How to Compile Java Online
- 1
Open Main.java
This page loads public class Main with Hello World.
- 2
Edit main()
Add statements inside main. Keep one public class in the file.
- 3
Run
Press Run or Ctrl+Enter to compile and execute.
- 4
Read output
See System.out on the right, or the compile error if javac fails.
Practical uses for an online Java IDE
- Verify Hello World before a lab machine has a JDK.
- Check a loop, array, or String method without creating a Maven project.
- Paste a short class from a textbook and run it.
- Jump to Python or C++ from the same toolbar when the course uses more than one language.
Why Choose Hemiley?
Hemiley targets the exact query “java compiler online”: a Main class, a Run button, and console output — not a full enterprise IDE.
The same layout as our Python and C++ compilers so mixed-language courses stay consistent.
Related Free Compilers
Frequently Asked Questions
Yes. Free to compile and run short programs with no sign-up.
The starter uses public class Main, which is what most tutorials expect. You can keep that. A different public class name is also accepted.
The sandbox compiles with JDK 21.
This compiler is for a single source snippet. Skip package declarations for the most reliable run.
Import java.util.Scanner, read from System.in, and put the typed values in Input before you press Run.
No. It is sent only to compile and run this attempt, not saved as a Hemiley project.
Read the message on the right. Common issues are a missing brace, a typo in main, or code outside the class.
Yes. The browser is the IDE for this snippet workflow.