Hackerrank is a great site I have recently discovered, with many programming exercises for new and experienced developers.
The exercises are not created strictly from programming languages, but the user can find a broad collection of interesting topics like Artificial Intelligence, Security, Mathematics and much more.
I have tried the Java route for a couple of days and I've managed to accomplish the results you can see in these screenshots :
Considering that at the Geek area the contestants are around 621, this place me at the first 10% for the Java Language for the Greek area.
I hope that you find this link interesting since you can test your abilities upon any programming language and even use the results somewhere for example inside your CV.
Of course there are other programming exercise sites like this one and I have tried many of them but for some reason I believe that this is the best one.