java-decompiler/jd-gui

JD-GUI is a standalone desktop application that lets you look at the source code of a compiled Java program. When Java code is compiled, the source files turn into .class files, which are not directly readable. JD-GUI reverses that process, called decompilation, and shows you a reconstructed version of the original Java source. The result is not always identical to what the developer originally wrote, but it is close enough to read, navigate, and understand the program's structure. The user interface is simple. You open a .class file or a .jar archive through the File menu, the Recent Files list, or by dragging files in from your file manager. JD-GUI then displays the reconstructed source, and you can browse through the methods and fields of each class. The README explains how to build the project from source. After cloning the repository you run the included Gradle wrapper with ./gradlew build, which produces a runnable JAR file along with platform-specific bundles: a Windows zip, a macOS tar archive, and Debian and RPM packages for Linux. Launching JD-GUI is a matter of double-clicking the JAR, the jd-gui.exe on Windows, or the JD-GUI application on macOS. From a terminal you can also start it with java -jar jd-gui-x.y.z.jar. The project supports extensions: extra JARs can be passed on the classpath when starting the app to add functionality. Helper Gradle tasks generate IntelliJ IDEA and Eclipse project files for developers who want to work on JD-GUI itself. Uninstalling is described as deleting the JAR and the jd-gui.cfg configuration file, or dragging the application to the trash on macOS. JD-GUI is part of a wider Java Decompiler project (linked from the README as java-decompiler.github.io) and is released under the GNU GPL v3 license. The README also includes PayPal links for donations in euros or US dollars.