Note that by using a technique known as escape analysis, a virtual machine like the JVM can detect that the lifetime of an object is such that it doesn't leave the context of a particular method and then stack-allocate the object implicitly. That may seem like a limited optimization, but when you combine it with method inlining it gets a lot more useful. I believe the optimization is turned off by default in the Sun/Oracle JVM but can be enabled via the -XX:+DoEscapeAnalysis option. For programs that allocate large numbers of short-lived objects, it can make a significant performance difference.

Note: If you use scala, escape analysis can be particularly helpful. The "pimp my library" pattern for extending classes involves creating wrapper objects, and these can often be optimized away. http://www.decodified.com/scala/2010/08/27/scala-rich-wrappi... has more details

Often that allocation should be free - when you do a "proper" function call you'll be increasing that pointer already, and the total size of stack-bound objects in many functions can be determined at compile time.

(Erm... I think. Need to read more...)