This program show how to use map in Java
This program keeps a map in which the keys of the map are objects of class Employee. An employee should have a first name, a last name, and a unique integer ID. For the performance changes and removals, lookup should be by ID. Prompt the user of the program to add or remove employees, to modify the performances, or to print all the performaces. The printout should be sorted by last name. If two employees have the same last name, then use the first name as a tie breaker. If the first names are also identical, then use the integer ID. Supply compatible hashCode and equals methods to the Employee class. Test the hash code by adding the Employee objects to a hash set.