In this paper, we report on the experiences we had and the problems we encountered integrating dynamic object extension in Java. At first sight, this seems impossible due to the incompatibilities between the classbased and the prototype-based paradigms. Even more, because the Java virtual machine is tightly coupled to a class-based language, our goal seems impossible. Weshow, however, that dynamic object extension can be incorporated into a class-based language and compiled to the Java virtual machine, although some compromises need to be made.