To practice algorithms, I've been using some technical interview web sites for good ideas. Here is one site I use: Ace The Interview - Technical Questions
The answers are posted in C/C++, but I code the answers in Java. They have some good algorithm questions there. Another site I use is: Technical Interview Questions
. The questions can usually be solved and coded within a few hours (depending on your Java proficiency).
One other suggestion I have is to port something? Do you have an old application you developed that you could port to Java? While you wouldn't be working with algorithms, you would certainly learn the API!!