I have just completed to write the Israeli Guide to J2ME. It is a freeware tutorial for learning J2ME. It is available for free personal and academic usage. The tutorial focuses on J2ME (CLDC/MIDP). You can find it on-line at http://www.zindell.com/israeliJavaBookME/ch1.htm.
The Visitor Design Pattern
The visitor design pattern allows us to add operations to objects that already exist without modifying their classes and without extending them.