Java performance improvement and pitfalls:
The other area is architecture. Sometimes poor performance is literally "built in" to an application, making it very difficult to do any useful performance improvement by tuning. For example, suppose that you make heavy use of the object-oriented paradigm, such that you have many layers of superclasses and subclasses.
Moreover, suppose your application is one that processes bytes or characters one at a time, and each byte is processed through all these layers of classes and methods. In such a case, adequate performance may beimpossible to attain, short of an application re-design.
It’s important to keep performance in mind when designing your applications.
see: http://www.glenmccl.com/jperf/