SwingX
· Contains extensions to the Swing GUI toolkit, including new and enhanced components that provide functionality commonly required by rich client applications.
Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window swingx-project-1.6.2-2.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.