Interface is an integral part of java and has become so powerful over the years, that it shifted the way a Java programmer thinks.
To use the partitioningBy Collector, you have to pass the Collectors.partitioningBy in the collect() method of Stream API.
how you can iterate over a List, be it ArrayList, LinkedList or any other. Basic loop to iteration to Stream API. And also, figure out which one is best suitable for our code.