Transformations can be written in Java or CloverDX transformation language (CTL):
Java can be used in all components.
Transformations executed in Java are faster than those written in CTL. Transformation can always be written in Java.
CTL cannot be used in JMSReader, and JMSWriter.
Nevertheless, CTL is very simple scripting language that can be used in most of the transforming components. CTL can be used even without any prior knowledge of Java.