public class MultipleExternalSortedFilesTableInput
Table input built from multiple files of NewRowEventsWrapper.
The files provided in the constructor should have the values sorted.
A priority queue will be used to store the values read from the list of files.
The priority queue will sort the values and this input class will provide the NewRowEvent from this priority queue.
next row is taken from the priority queue by polling the priority queue which returns the top FileWrapper.
On the topmost file wrapper, the poll method will be executed (which returns the top NewRowEvent) and, if not empty, the
file wrapper is re-introduced into the priority queue (so that he participated in the next newRow() operation )