Garbage First

The new garbage collector that we're currently developing called Garbage First or G1 for short. G1 straddles the young generation - tenured generation boundary because it is a generational collector only in the logical sense. G1 divides the heap into regions and during a GC can collect a subset of the regions. It is logically generational because it dynamically selects a set of regions to act as a young generation which will then be collected at the next GC (as the young generation would be). G1 can choose the regions with the most garbage to collect first (Garbage First, get it?) so gets the biggest bang for the collection buck.
(c) Jon Masamitsu, Our Collectors
That G1 is now a part of JDK 7.


Object emission matters

When we go looking at java performance, there are really 2 areas of the runtime that matter: the JIT and the GC. The job of the JIT is to make the code that is running execute as fast as possible. The GC is designed to take as little time away from the executing of code as possible (while still managing memory). Thus java performance is all about making the JIT generate more optimal code (more registers helps), and reducing the time the GC has to use to mange memory (bigger pointers makes this harder).