What is a memory leak in Java? What algorithm is used to find it?

Memory leak in Java is a situation where objects that are no longer needed by the application remain accessible through references and cannot be collected by the garbage collector, leading to increased memory consumption and potential OutOfMemoryError.

To find memory leaks, the following steps are usually taken:

1. Take a heap dump using tools like jmap.
2. Analyze the heap dump in profilers such as Eclipse MAT or VisualVM to find objects that occupy a lot of memory and are not released.
3. Determine the reference chains that hold objects and understand why they are not being removed.
4. Fix the code by removing unnecessary references (e.g., closing resources, clearing collections).

Algorithmically, this reduces to analyzing the object graph and searching for roots from which objects are reachable but should not be needed by the application.