Michael Kölling
Michael Kölling is a German computer scientist , best known for the development of the BlueJ and Greenfoot educational development environments and as author of introductory programming textbooks . 
<triplet> Michael Kölling <subj> BlueJ <obj> notable work <triplet> BlueJ <subj> Michael Kölling <obj> developer <triplet> Greenfoot <subj> Michael Kölling <obj> developer