There are a few people that are really knowleadgeable about Java, and Cliff Click is certainly one of them. One of his latest talks was at Devoxx and it's named "A JVM Does That???". Youtube link below.
This talk is so rich with content that it's hard to explain what it is about, so I'm just going to mention my favorite parts, but please watch it all if you haven't done so yet.
The explanation on the endless loop of GC cycles when have a cache (data structure) near the limit is just divine:
Or how about the illusion that locks are fast (and fair)
hence the importance of starvation-free locks that I mentioned in my CppCon talk, and the reason behind Andreia and I spending some of our time coming up with new starvation-free lock algorithms like Tidex:
The part about thread priorities is a nice demonstration of why lock-free and wait-free algorithms are so important (you don't need to care about thread priorities with lock-free and wait-free):
But my favorite is the fact that System.currentTimeMillis() has happens-before guarantees across cores on the HotSpot JVM, because this guarantee allowed us to make a blazing fast queue (which we will show in a future post):
Learning is fun with Cliff Click!