The system should have three classes: Computer, PC and Mac. Computer is the parent of other classes.

Computer defines certain fields, such as year(int), os_version(string) and brand (string). These variables have their setters and getters defined.

PC, has an extra field of OS (string) which can either be 'Linux' or 'Windows'. Use exception handling to prevent other values.

Mac has an extra field named Retina (boolean), which is either true or false depending on the display type the Mac has.

Once you create these classes write your test class with main method. Create PC and Mac objects, Assign them into a Computer array of 2 elements. Then use a for loop to display their information.