Hi, Seán here. I worked in industry for 13 years in FinTech and Telecoms. I have been a lecturer since 2002 and have a PhD in IT.  I am Oracle certified in Java to both OCA and OCP levels. I have taught the OCA/OCP syllabii since 2013 on a Level 9 Masters course on behalf of Ericsson. The popular Java certification tool Enthuware link to my YouTube channel in their explanations. I have recently co-authored (with Maaike van Putten) two books on Java: "Learn Java with Projects" and "Java Memory Management: A comprehensive guide to garbage collection and JVM tuning".