Miguel Paraz saw my TODO on finding a Java interpreter and he pointed me to Beanshell. I've been thinking about using a Java interpreter in my introductory computing class in order to help my students grasp Java concepts more easily. Students can use the Beanshell interpreter to explore arithmetic expressions, variables, input (through JOptionPane), Boolean logic, ifs, loops, and even a little bit of object-oriented programming.
It's an experimental technique, and I have some concerns regarding the transfer of knowledge. I need to make sure that they'll be able to work with standard Java programs well.
Another interactive Java environment I want to explore is BlueJ. It's explicitly designed for introductory computing and it emphasizes object-oriented programming.
With only a few days before the start of classes, I do not think I'll be able to prepare well enough to use either environment next sem. However, I would like to experiment this summer, if we are still offering CS21A then.