We argue that Java is a natural language to develop interactive teaching material that can be shared and distributed widely. Unlike any other programming language or platform we know, Java development is justified because of its almost universal acceptance. We develop a block diagram (BD) based approach that allows one to develop interactive and downloadable signal processing laboratories. As an example, we show how specific experiments for a DSP class, as well as for an advanced course on wavelets have been developed. The article first explains why the Java language has been chosen, and then describes what has been realized today. Finally, we show how the BD representation can be efficiently used for the development of a wavelet theory course. It is shown that only a few simple blocks are sufficient for creating many didactic programs. This can be seen as an a posteriori justification of the BD model.