Having just gotten into Java from hacking Perl nonstop for quite some time, what worked for me was:

Understand objects: First, read Object Oriented Perl as the previous example suggests. Go through the examples and really understand what Conway is saying. (It doesn't hurt that it's a fun read.) Next, write some code yourself -- either subclass someone else's objects and play around or create your own. (Perl makes this simple!)

Read a good Java book: For me, this was Thinking in Java by Bruce Eckel. By "good Java book" I mean one that doesn't try to do the "...in n (days|hours)" route but teaches you about how the language works at a fundamental (thinking) level. YMMV with this book, but it worked well for me.

Good luck! And remember that everything has its place :-)