The descendingMap() method of the NavigableMap interface returns a navigable map according to the descending order of keys. This method returns a map that is similar to the result of the Collections.reverseOrder(comparator()) method. The expression m.descendingMap().descendingMap() returns a map exactly equal to map m.
The descendingKeySet() method of the NavigableMap interface returns a navigable set according to the descending order of keys in the map. The navigable set obtained as a result of the descendingKeySet() method supports element removal via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. However, it does not support the add and addAll operations
The File class is an abstract class used for file operations such as creating empty files, deleting files, searching for a file in a directory, making directories, etc. It does not contain any method to read or write data from a file. The File class extends the Object class and implements the Serializable and Comparable interfaces.
The FileReader class provides methods for reading character files. It contains methods for reading a single character, a fixed number of characters, or a whole stream of characters. Since these classes do not provide fast performance, they are usually wrapped within high-level reader objects such as a BufferedReader