Thanks for the memory. The Java heap, where every Java object is allocated, is the area of memory you're most intimately connected with when writing Java applications.
The JVM was designed to insulate us from the host machine's peculiarities, so it's natural to think about the heap when you think about memory. You've no doubt encountered a Java heap OutOfMemoryError — caused by an object leak or by not making the heap big enough to store all your data — and have probably learned a few tricks to debug these scenarios. But as your Java applications handle more data and more concurrent load, you may start to experience OutOfMemoryErrors that can't be fixed using your normal bag of tricks — scenarios in which the errors are thrown even though the Java heap isn't full.
When this happens, you need to understand what is going on inside your Java Runtime Environment (JRE). Decorators make magic easy : IBM. DeveloperWorks charming python.