I want to use a Java app on my ecommerce site, but only if it will improve my rankings with Google. So, can Google search content that appears in Java?
As Google says, search engines are basically text based. You can add elements such as Java or flash in your website BUT you need to provide text or that page should be available in text format
Read Flash, images, and other non-text files from Google Webmaster http://www.google.com/support/webmasters/bin/answer.py?answer=72746&query=flash&topic=&type=