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Java Online Runner
Need a full server-side compile environment? Go to Java Online Compiler
Initializing runtime environment… 0% First run compiles Java in-browser; may take 10~30s, please wait
Code
What is Java Online Runner?
This tool is powered by CheerpJ, a Java Virtual Machine compiled to WebAssembly. It compiles and runs Java source code directly in the browser with a full OpenJDK runtime. No JDK installation and no server are required.
Key Features
- In-browser compilation: a built-in javac compiler (ECJ) compiles your source inside the browser, consistent with a local environment.
- Ready to go: the first load downloads about 20MB of runtime resources which are then cached.
- Output capture: System.out and System.err output is shown in real time.
How is this different from the server version?
We also provide a Java Online Compiler with JDK 8 / JDK 21 versions. Use the browser version for lightweight learning and quick testing, and the server version when you need a specific JDK or heavy dependencies.
Usage
- Type or paste Java code (a class with a main method).
- Click Run to compile and execute.
- Compilation errors and output appear in the output panel.