To automate your trading using Dukascopy's JForex platform you'll need to learn how to program using the Java language. This language is derived from C and C++, so it too allows you to develop an objected-oriented system just like MQL5 and C#. The language was originally created by Sun Microsystems, who have recently been taken over by Oracle Corporation. There are vasts amounts of information available on the Oracle website, including numerous Java tutorials.

If you prefer to work your way through an eBook instead you can also download an "Introduction to Programming Using Java". This book was written by David J. Eck of the Hobart and William Smith Colleges, and you can access an online version of the book on their website, and also download the source code for all the examples.