Java JDK (Java Development Kit) is a special version of Java for developers, allowing you to write Java applications. It is needed in certain steps of Kotobee Author, such as creating a random keystore for your Android mobile app. The standard Java which you probably already have, is named Java JRE (Java Runtime Environment).
Although installing Java JDK is fairly easy, the installation can sometimes seem to take no effect, particularly on Windows. This may be due to the existing Java version (JRE) still being referenced, instead of Java JDK. This can be fixed by following some simple steps, to edit your environment variables, specifically the Path variable.
Java JDK may be downloaded from here:
This video tutorial will walk you step by step through installing Java JDK, and show you how to set environment variables appropriately.