A midlet is a piece of Java software specially dedicated to mobile phones or resource limited devices.
Although written in Java, they are not supposed to be played on a regular computer because the libraries they rely on are not the same (to make it very very simple).
However, different projects aim to recreate the underlying libraries so that a midlet can be played or tested with you computer.

This is the ideal occasion to demonstrate WapcamLet as an applet in your browser for testing two different such libs.