Vector are synchronized and array list are unsynchronized.Vector are most suitable when we handle with Multi threading.In Struts 1.2,Action are singleton ,work on multi threading.So for Struts 1.2 ,application Array list is suitable or Vector list
The term Singleton is vastly overused, a few lines of code in a large program that is only used once is a candidate for just unrolling the loop and placing the code directly in the instruction stream. Doing so avoids several issuse that in compiler design may become nasty in unrecognized ways.
If your data structure is exposed to more than one thread, use synchronized data structures. To do otherwise is speculative.
"The differential equations that describe dynamic interactions of power generators are similar to that of the gravitational interplay among celestial bodies, which is chaotic in nature."
Normally if you have a List of something, it should be stored in the ActionForm, not the Action. ActionForm classes are not multithreaded. Furthermore, if you want to make an ArrayList Synchronized, you can with the following code: