This week's book giveaway is in the Testing forum. We're giving away four copies of Data Structures the Fun Way: An Amusing Adventure with Coffee-Filled Examples and have Jeremy Kubica on-line! See this thread for details.
Typically dynamic arrays are not used in Java because ]the standard API provides the Collections Framework, which provides many dynamically sized data structures. This leads me to suspect that you are doing something for a homework assignment. So what exactly are you trying to accomplish and how do dynamic arrays fit into the picture? If you can ask a more specific question, I can probably give a more specific answer. See this page in our FAQ for some tips on what details to include when you ask a question.