Java Compiler

Most people learning Java do not need a full IDE with a project wizard, a build system and forty panels. They need somewhere to type a class, a key that runs it, and an honest account of what went wrong.

This is that. It opens a .java file, colors it properly, runs it with a keypress and shows you what the program printed — in one window, with nothing to set up.

This app is for Java: classes, objects and public static void main. JavaScript, the language of web pages, only shares the name, and it has an app of its own.

OpenJDK 25 ships inside the app. On a PC that has never had Java, your first program runs immediately: no JDK download, no JAVA_HOME, no PATH. Each file runs on its own, the way Java runs a single source file, so there is no project to create before you can start.

If you already have a JDK, Settings will use yours instead.

Syntax color, folding, bracket matching and completion that knows Java's keywords and the classes you reach for first — Scanner, ArrayList, HashMap, String. A tab per file, each with its own undo.

F5 compiles and runs. Output arrives in the panel as it is printed, and when your program asks for input through Scanner you answer it right there. Ctrl+F5 feeds it input.txt from the same folder instead, the way contest problems are practiced.

A compile error becomes a line you can click, with the same error in a sentence underneath: what "cannot find symbol" usually means, why main cannot call a method that is not static, what a missing return is complaining about.

Exceptions get the same treatment. A NullPointerException, an ArrayIndexOutOfBoundsException or a Scanner that was handed the wrong kind of input is explained in plain words, with the line it happened on.

The assistant panel can see the file you are on. Select some lines and it sees those too; run something that fails and the error goes with your question.

No AI service is included with this app, and none is being sold to you here. The assistant is inert until you enter an API key of your own, and the price of this app buys the editor and the JDK — not the model behind that key. Whatever you spend asking questions is billed to you by the provider you chose, on your own account, and never passes through us.

Bring a key from Claude, ChatGPT, Gemini or OpenRouter, or point it at Ollama or LM Studio on this PC and it works offline. The key is kept on this PC, outside the settings file.

Fifteen snippets in four sections: basics, objects, collections, and files and more. Reading input safely, loops, arrays, methods, classes, records, inheritance, lists, maps, streams, files, random numbers and a small guessing game. Each opens in its own tab as a complete program you can run before you change a line.

It is an editor and a runner, not a full development environment. There is no debugger, no Maven or Gradle, and each file runs on its own rather than as a multi-module project.

No account. No sign-in. No ads. The app makes no network call of its own; the only thing that ever leaves your PC is a question you type into the assistant, going to the provider whose key you entered, or feedback you choose to send.

Built for Windows 11, and at home on Windows 10.