In this task, you are required to provide complete class definitions and then create instances of various classes and use methods to perform various tests.

(a) Define an abstract class called Staff with the following fields and methods:

Fields: name, id, position representing the name, staff id and the position of a staff member in an organisation. Encapsulation should be used to protect these fields against intentional or accidental, direct modification

Constructors: a no-args/default constructor, and an overloaded constructor to initialise the fields to appropriate values when the instances of the class are created

Methods: a toString() method to print a string representation of the objects, get and set methods to provide access to each of the three fields

(b) Define a subclass of the Staff class called FullTimeStaff with the following additional field and methods:

Field: researchArea,a string variable representing the research are of the staff member. Again, encapsulation should be used to protect this field against intentional or accidental, direct modification

Constructors: a no-args/default constructor, and an overloaded constructor to initialise the fields to appropriate values when the instances of the class are created

Methods: a toString() method to print a string representation of the objects, additional get and set methods as required to provide access to the field

(c) Define a subclass of the Staff class called PartTimeStaff with the following additional field and methods:

Field: timeFraction representing the time fraction of a part-time staff member. This would be a number between 0.1 and 1.0. Again, encapsulation should be used to protect this field against intentional or accidental, direct modification

Constructors: a no-args/default constructor, and an overloaded constructor to initialise the fields to appropriate values when the instances of the class are created

Methods: a toString() method to print a string representation of the objects, additional get and set methods as required to provide access to the field

(d) Define another subclass of the Staff class called CasualStaff with the following additional field and methods:

Field: hours representing the number of hours that the casual staff member works at the organisation. Again, encapsulation should be used to protect this field against intentional or accidental, direct modification

Constructors: a no-args/default constructor, and an overloaded constructor to initialise the fields to appropriate values when the instances of the class are created

Methods: a toString() method to print a string representation of the objects, additional get and set methods as required to provide access to the field

(e) Finally, define another class called TestStaff with a main() method to perform necessary testing for the classes defined in the previous sections. In the main method, write the code to: (1) create an ArrayList object to store references to Staff objects; (2) open a text file named staff.txt (available on interact resources), which contains data relating to staff members, create FullTimeStaff, PartTimeStaff and CasualStaff objects based on the first field in each row in the file (full, part, or casual); (3) add these objects to the ArrayList; and (4) test various methods of the objects using loop(s) and methods as necessary, including the code to:

Repeatedly display a menu of five options (1, 2, 3, 4 and 5) such that

Option 1 will display details of only full-time staff

Option 2 will display details of only part-time staff

Option 3 will display details of only casual staff

Option 4 will display details of all staff

Option 5 terminate the program