The java virtual machine recently introduced a very interesting optimization that allows to eliminate some object allocations. This optimization is called scalar replacement and depends on escape analysis. You can read more about it in an article by Brian Goetz.
Simply spoken when an object is identified as non-escaping the JVM can replace its allocation on the heap with an allocation of its members on the stack which mitigates the lack of user guided stack allocation. The optimization is enabled by default since JDK 6U23 in the hotspot server compiler.