Java Development Kit. In order to compile any Java code you will require the Java Development Kit, or JDK. This is different from normal Java, so even if you have Java you may still need to install the JDK. If you have ever made a plugin, then there is no need to worry as you already have the JDK installed. You can grab it from here: http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html