When you run a "converted" VXP file, you are actually running an interpreter that loads the Java JAR resource embedded inside the VXP container. This is similar to how some game consoles run retro games. The "converter" simply packages the JAR and the interpreter together into a single VXP.
In the age of Android and iOS, it is easy to forget the rich, chaotic ecosystem that preceded them. Before smartphones became ubiquitous, "feature phones" dominated the market. Brands like Nokia, Motorola, Sony Ericsson, and Samsung produced millions of devices running proprietary operating systems. Among these, the most popular platform for mobile gaming and applications was Java ME (Micro Edition), commonly known as J2ME. Apps built on this platform had the .jar or .jad extension. java to vxp converter