Java online compiler

What runs your code

Good to know

• Your file runs with the source launcher, java code.java, so there is no separate compile step and the class can have any name, such as Main.
• The JVM sees 2 CPUs and may use up to 60% of the 512 MB for its heap.
• Starting the JVM and compiling take about 2 seconds, so a short program takes that long too.

Run Java from your own code

Send the code and its input to the sync endpoint with an API key, and the output comes back in the response. The API docs cover the async endpoint with callbacks and every response field.

curl -X POST https://api.onlinecompiler.io/api/run-code-sync/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "openjdk-25",
    "code": "import java.util.Scanner;\n\npublic class Main {\n    public static void main(String[] args) {\n        String name = new Scanner(System.in).next();\n        System.out.println(\"Hello, \" + name + \"!\");\n    }\n}",
    "input": "Ada"
  }'

The response has output ("Hello, Ada!\n" here), error, exit_code, time and memory.

Put a runnable Java example on your site

The editor above is the embeddable widget. Add the script and a div with your widget key, and your readers can edit and run the code without an account:

<script src="https://onlinecompiler.io/widget.js"></script>

<div class="runcode" data-key="YOUR_WIDGET_KEY" data-lang="openjdk-25">
  <script type="text/plain">
    import java.util.Scanner;

    public class Main {
        public static void main(String[] args) {
            String name = new Scanner(System.in).next();
            System.out.println("Hello, " + name + "!");
        }
    }
  </script>
</div>

On a platform that takes an iframe but not a script, such as many course sites, use the iframe embed. For Docusaurus, MkDocs, Sphinx and Mintlify, see runnable code examples in docs.

Other languages

Python, C, C++, C#, F#, Go, Rust, PHP, Ruby, Haskell, TypeScript.

Frequently asked questions

Is this Java online compiler free?

Yes. Running Java on this page needs no account and shows no ads. To run Java from your own app or site, the API and the widget are free up to 100,000 runs a month, commercial use included.

Can my Java program read input?

Yes. Type it in the Input tab before you run, and the program reads it from standard input. The whole input is sent when you press Run, so a program can't ask for more while it runs.

Can I use Java libraries?

The Java standard library. There is no Maven or Gradle, and programs have no network access to download jars.

How long can a program run?

Up to 30 seconds, with 512 MB of memory and 2 CPUs. A program still running at 30 seconds is stopped with exit code 124, and output over 64 KB per stream is cut.

Where does my code run?

On our servers, in a fresh gVisor sandbox with no network access that is deleted when the run ends. Each run is kept in execution history with its output; the security page says what is stored.