billing
· GetApps IAP is a revenue-enhancing service for developers. Accessing GetApps IAP SDK enables your app to offer in-app purchasing service to your users.
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 billing-1.0.9.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.