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Online Java Playground

Runs on OpenJDK 13.0.1 · Free · No signup required

A free online Java playground and compiler for backend engineers. Write Java, compile it, and run it in your browser — no JDK install, no IDE, no project scaffolding, no signup. Java's setup overhead is the main reason people avoid quick experiments in it, which is exactly what this removes. Use it to test how a stream pipeline evaluates, check what a collection returns on an edge case, confirm the behaviour of an exception you are about to catch, or work through interview-style problems without opening IntelliJ. Compilation and execution happen server-side against a real JDK, so compiler errors match what you would see locally. Standard input is supported. Your class should be declared as shown in the starter snippet. If you are preparing for Java backend interviews or building Spring services, the playground connects to our Java projects, interview prep and bootcamp track.

Java Playground — Frequently Asked Questions

Do I need to install the JDK?
No. Compilation and execution happen on our servers. A browser is all you need.
Can I use Spring or external libraries?
No. The playground compiles single-file programs against the standard library. It is built for testing language behaviour and practising problems.
What should my class be called?
Follow the starter snippet's structure. The main method must be present for the program to run.

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Ready to build real backends rather than test snippets? Explore backend engineering courses and projects at MasteringBackend.