We know that a memory leak can occur in Java applications when object references are unintentionally held onto after the references are no longer needed. Typical examples of these are large collection objects, a unbounded cache, large number of session objects, infinite loops etc. A memory leak results in a OutOfMemoryError.Besides this core reason, there are other factors that may also result in a OutOfMemoryError exception
1. Java heap fragmentation: Heap fragmentation occurs when no contiguous chunk of free Java heap space is available from which to allocate Java objects. Various causes for this problem exist, including the repeated allocation of large objects (no single large fragment in first generation). In this case, even if we see good amount of free heap, memory allocation fails.
2. Memory leaks in native heap. This problem occurs when a native component, like database connections, is leaking.
3. Perm size has exhausted. The permanent generation of the heap contains class objects. If your code is using a lot of reflection/introspection, then a number of temporary class objects are created that would exhaust the perm space. More info can be found here.
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You can prevent memory leaks by watching for some common problems. Collection classes, such as hash tables and vectors, are common places to find the cause of a memory leak. This is particularly true if the class has been declared static and exists for the life of the application. . The prevalence of memory leak bugs has led to the development of a number of debugging tools to detect unreachable memory. Coverity Prevent is one of the tool that you can use for fixing these kinds of bugs. Coverity Prevent is also used by the Department of Homeland security to scan many open source projects. You can get more info at http://www.Coverity.com
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