Well, there are three sorts of Java the normal consumer should care:

1. Android Java, running on top of its own virtual machine (aka Dalvik). As long as you do not have Android, you can disregard this variety.

2. JavaME also known as MIDP, also known as J2ME, also known as PhoneME is a somewhat lobotomized version of Java supported by most mobile phones. Most mobile games and some mobile apps running on dumb phones are written using this version of Java.

3. JavaSE is the desktop Java. If you ever run a Java application on your PC or Mac, or a Java applet in your browser, it is most likely written in JavaSE. The number of widely used Java applications is near nil though, mostly due to problems with performance, compatibility, and maintenance, so you are unlikely to ever use this one.

Of these three, only #2 (JavaME) is of practical interest to a big number of users, because everybody is used to MIDP games on their phones. Unfortunately, there is still no standalone JavaME package for the tablets, that would instantly allow users to play .jar and .jad files with MIDP games.