Write and run Java in your browser instantly — no JDK, no signup, works on any device including Chromebooks. Free online Java IDE for AP CSA and beyond, with lambdas, streams, a debugger and live collaboration.
Common questions
Is the CS++ Java IDE free?
Yes. The Java IDE is completely free to use. You can write, run, and auto-test Java in your browser at no cost, and you can start without creating an account.
Do I need to install a JDK or log in to run Java?
No. There is no JDK, plugin, or download to install — the IDE runs Java on a custom in-browser interpreter inside a Web Worker. You can start coding immediately without logging in. Signing in is optional and only adds cloud save so your code follows you across devices.
Does it work on Chromebooks and other school devices?
Yes. Because everything runs in the browser, the Java IDE works on locked-down Chromebooks, iPads, phones, Macs, and Windows PCs — no admin rights, installs, or Linux container needed. It is a good fit for school networks where students cannot install software.
Is it good for beginners and AP CSA students?
Yes. Beginners get clear error messages, a step-through debugger, and a quiet editor without the noise of a full professional IDE, and AP Computer Science A (AP CSA) students can practice everything the exam covers — types, loops, methods, Strings, arrays, ArrayList, 2D arrays, classes, inheritance, and recursion. When the course ends, the same IDE keeps going: generics, the collections framework, lambdas, and streams.
What does the in-browser interpreter support — does it run full Java?
It runs most of the Java language and the core of the standard library, though not every class in the JDK. That includes classes, interfaces, abstract, inner and anonymous classes, generics, your own exceptions and try-with-resources, the java.util collections (ArrayList, LinkedList, HashMap, TreeMap, HashSet, TreeSet, ArrayDeque, PriorityQueue, List.of and more, with Arrays and Collections), lambdas, method references, streams, Optional, regular expressions in the String methods, printf formatting, and Scanner input. It is tested against the real JDK, so programs print what Java prints. Out of scope: threads, writing files, reflection, enums, and newer syntax such as records and switch expressions. A companion reference page at /java-ide/reference lists exactly what is supported.
Can teachers use it in the classroom?
Yes. Teachers can share starter code and worked examples via shareable links, have students run and auto-test Java on any device, and use it for in-class demos and homework. It comes from CS++, founded by a 20+ year AP CS teacher, and is designed around how AP CSA is actually taught.