Returning a subclass as type interface

I am having a problem with a class I am writing for an assignment. I have an interface, Person, that has 3 abstract methods getID, getFirstName, and getLastName. These return Strings. I have another class called Employee which implements Person. I have a static method, which takes in a line from a file as a String and instantiates a new object of Employee then returns it as a Person. The only problem is that Employee also has an attribute called salary that Person cannot have, so later when I try to manipulate data on the new objects, I cannot access the salary attribute in the objects. I really don't know any way around this. If any of you can give me any suggestions on this, it would be greatly appreciated. Below you can find the parse method, and the stream I used to create the list, the stream where I attempted to manipulate the salary data, and the interface.

public static Person parse(String s) { 
    String[] empData = s.split(","); 
    Employee hello = new Employee(empData[0], empData[1], empData[2], BigDecimal.valueOf(Double.parseDouble(empData[3]))); 
		
    return hello;
}  

List<Person> stream = Files.lines(Paths.get(fileName)) 
	.map(Employee::parse)
	.collect(Collectors.toList()); 

DoubleSummaryStatistics total = stream.stream().mapToDouble((emp) -> Double.parseDouble(emp.salary.toString())).summaryStatistics(); 
			System.out.println("Total average and the total number of employees:"); 

import java.math.BigDecimal;

public interface Person {
	public String getID(); 
	public String getFirstName(); 
	public String getLastName();
}

> which takes in a line from a file as a String and instantiates a new object of Employee then returns it as a Person.

Doctor, it hurts when I press here!

Well, stop doing that then.

Return this as a List<Employee> instead. The whole point of returning List<Person> is that you are free to change your mind later and return non-employees (you have signed up to always return persons, but not neccessarily employees), therefore, javac will not let you presume that they are employees. If you want to carry on and assume: Hey, these are always employees, therefore 'person.getSalary()' is always going to be sensible, then... say that.

If you can't, you can use instanceof to check if a person is an employee, and then cast to get the salary:

double salary = p instanceof Employee ? ((Employee) p).getSalary() : 0.0;

and starting in java15, you can write:

double salary = p instanceof Employee e ? e.getSalary() : 0.0;

which is a lot prettier...

but that's a very different kind of code: That's saying: For all persons, IF they are employee, consider their salary to be whatever the employee object says it is. If not, then count them at 0. If that's what you WANT, this code works, but it sounds more like you're confused. Do you have a list of persons, or a list of employees, which one is it?