$1.$ Write the code for the Customer class.

$2.$ Don't duplicate any code between the constructors.

$3.$ Implement the precondition: customer numbers must be in the range $1000-9999,$ inclusive.

Working with this class you must strongly follow the Rules for Creating New Classes.

Don't change given methods, variables, and types. Follow the UML class diagram.

Don't worry about comments, JavaDoc tagging, typical course Style Guide rules