Memory leak in Java is when an object is no longer being used but unable to be garbaged collected because it is still being referenced some other places in the application. As a result, this unused object is occupying the memory resource even though it is not being used by the application. You application will eventually crash if too much of these unused objects piled up to the point there is not enough memory left for other active objects in your application. You will see crash with out of memory error.