David Barnes is a Lecturer in Computer Science at the University of Kent, in Canterbury, England. He has been teaching introductory programming for over 25 years, and has practical experience of a wide range of programming languages. He has been teaching object-oriented programming in Java for over 10 years. David is passionate about the excitement that is inherent in computer science and is actively involved in promoting it as a subject area to high-school children. In addition to computing education, his main research is in the area of software engineering.Michael Kï¿½lling is a Senior Lecturer at the Computing Laboratory, University of Kent, in Canterbury, England. He holds a PhD in computer science from Sydney University, and has worked in Australia, Denmark and the UK. Michael's research interests are in the areas of object-oriented systems, programming languages, software tools, computing education. He has published numerous papers on object-orientation and computing education topics. Michael is one of the developers of BlueJ and, more recently, the Greenfoot platform.