Java Memory Leaks occur when objects still have a GC root reference, but are not actually used anymore. Those “Loitering Objects” stay around for the whole life of the JVM. If the application is creating those “dead objects” on and on, the memory will be filled up and eventually result in a java.lang.OutOfMemoryError. Typical causes are static collections, which are used as a kind of cache. Usually objects are added, but never removed (Let’s face it: How often have you used add() and put() and how often used remove() methods?). Because the objects are referenced by the static collection, they cannot be freed up anymore, as the collection has a GC root reference via the classloader.
