java based programming challenges [closed]
Solution 1:
Project Euler
It's not Java specific, but a good Programming Challenge site for any language.
Solution 2:
The following sites have some good programming challenges. There is nothing like a challenge based on a language. Hope these links help you.
Top coder
Spoj
Project Euler
Code Chef
Solution 3:
I add CodingBat to the sites mentioned here. And project Euler get also my recommendation.