Please help with understanding the full code.

There is one service class for this assignment named Volunteer as defined in 2. Create service class. the Volunteer UML class diagram . Create this class based on the UML class diagram. Add edits to the set methods for the following conditions: first name cannot be null or have a length of zero; last name cannot be null or have a length of zero; start date cannot be null; volunteer hours can't be negative. Do not update the class variable if the values are invalid. There is one application class for this assignment named ManageVolunteers. 4. Create application class. Create this as a separate file from the Volunteer class file. This will be an application class so it will have the main method. 5. Write code in the application class to test the service class. The code below goes in the ManageVolunteers class. Volunteer - firstName : String - lastName : String - startDate : LocalDate - volunteerHours : double + DEFAULT FIRST NAME : String = "no first name assigned" + DEFAULT LAST NAME : String = "no last name assigned" + DEFAULT_START_DATE : LocalDate = current date + DEFAULT_HOURS : double =0 + Volunteer (firstname: String, lastname: String, start: LocalDate, hours: double) + Volunteer () + Volunteer (firstname: String, lastname: String) + getFirstName ( ) : String +setFirstName (newFName: String) : void + getLastName ( ) : String + setLastName (newLName: String) : void + getStartDate ( ): LocalDate + setStartDate (newStartDate: LocalDate) : void + getVolunteerHours ( ) : double + setVolunteerHours (newHours: double) : void + toString ( ) : String