Write Java in your browser. Editor is live today.
The Java editor is fully functional now: syntax highlighting, formatting, bracket matching, and persistent code state. Server-side execution is provisioning and will light up at this same URL when it goes live — no bookmark change needed.
What works today and what is coming
To be direct: the Monaco editor with Java syntax highlighting, code formatting, and localStorage persistence is live today. Clicking Run shows a 'server execution provisioning' message rather than output. That changes when the execution backend comes online — the URL, the editor, and your saved code all stay the same.
We chose to ship the editor first rather than wait for full execution to be ready. Candidates can write, format, and review their Java solutions right now. If you are practicing for an interview that uses Java, you can use this editor to structure your thinking and prepare your code, then test it in your local IDE or on LeetCode directly.
We also chose to be transparent about this rather than showing a spinner or a vague error. Other free online Java compilers are often available but they throttle execution, inject ads, or require a login. When execution lands here it will be free, unthrottled, and account-free.
Java 21 language features in the editor
The editor understands Java 21 syntax. Pattern matching for switch, sealed classes, record patterns, virtual threads, unnamed classes — all highlighted and formatted correctly. If you are studying for an interview at a company that uses a modern Java version, the editor does not hold you back to Java 8 syntax.
The formatter follows Google Java Style by default. Import statements are sorted, brace placement is consistent, and line length is managed. If you write a multi-method class with a few helper functions, the formatter organizes it in the style an interviewer would expect.
Autocompletion for Java keywords and standard library types is powered by Monaco's Java language service. You get suggestions for java.util types (ArrayList, HashMap, PriorityQueue, TreeMap), common import paths, and method signatures for the standard collections API.
Preparing Java solutions for algorithm interviews
Java is the language of choice at many enterprise companies and is accepted at virtually all major tech interview platforms. The verbose syntax can feel slower to write under time pressure than Python, which is why practicing with a proper editor — rather than a plain text box — builds the muscle memory for typing class boilerplate quickly.
The starter snippet in the editor is a two-sum solution using HashMap, which is among the most commonly asked problems in Java interviews. It demonstrates the import pattern, class structure, and the Java Collections API usage that interviewers expect to see.
A pattern many candidates use: write your solution in this editor (with formatting and syntax checking), then paste it into LeetCode or your company's interview platform. The transition is smooth because the editor produces clean, consistently formatted code.
No throttling when execution arrives
When server-side Java execution goes live, it will be unthrottled and free — the same model as the Python and JavaScript runners. We run the execution on a Piston-based backend that provisions language runtimes on demand.
Candidates who bookmark this page today will have a working Java execution environment the moment it goes live, without needing to do anything. The URL is permanent. The code you save in localStorage will still be there.
If you want to be notified when Java execution goes live, you can try the AI interview assistant — users with an account receive product updates. No account is required to use the editor.
Frequently asked questions
- Can I run Java code today?
- Not yet — the editor and formatter are live, but server-side execution is provisioning. Python and JavaScript run instantly today. Java execution will appear at this same URL when it goes live.
- Which Java version will be supported?
- Java 21 (LTS). The editor already understands Java 21 syntax including records, sealed interfaces, and pattern matching for switch.
- Why does it need a server? Python runs in the browser.
- Python runs in the browser via a WebAssembly port (Pyodide). The Java Virtual Machine is not available as a WebAssembly target in the same way, so Java execution requires a sandboxed server environment.
- Can I save my Java code now?
- Yes. The editor saves to localStorage automatically. Your Java solution will be there when execution goes live — you will not need to re-paste it.
- Will it be throttled or require an account?
- No. When execution launches it will be free and account-free, the same as the Python and JavaScript runners today.
- What is the catch?
- No catch. We give away the compiler to introduce candidates to our AI interview assistant. Use it forever for free.