The GUIKit` package can also be used to provide Wolfram Language-enriched user interfaces to standalone Java applications, leveraging the fact that J/Link also works within a Java application environment. There is a sample custom application Java main class that demonstrates this within the GUIKit.jar: com.wolfram.guikit.app.GUIKitApplication. You can run any of the GUIKit` definitions you build as standalone Java applications if you add all .jar files required by GUIKit` to the classpath and have the Wolfram Language installed on the machine that is running the application. Likewise, the entire standalone Java application does not have to be defined only by GUIKit`. You can easily load dialogs and panels built with GUIKit` to supplement your existing Java application.
There are sample Windows and Unix scripts located in the Examples/Standalone/ directory of the GUIKit` distribution that show typical complete runtime scripts using com.wolfram.guikit.app.GUIKitApplication.