For example, if you want to travel from country A to country C and there's stopoever at B (A->B->C), there'll be two segments reflected on the itinerary. The route is A to C.
So 1 segment is assoicated to 1 flight. But in my opinion, 1 flight can be associated to more than 1 segment.
fc_1 = new FileOutputStream(fileNameNormalized_1,true).getChannel();
fileSize_0 = (int)fc_0.size();