Java - set object attribute to null

Question

I try to implement an specification diagram. There are 3 classes: Company, Department, Employee.

• Employee has name, salary, department.
• Every Department has a Company, name, employees (0..n) - I made a LinkedList for that -, and a Manager of the Employee Type which can be manager in only one department.

• Departments can have subdepartments of the Department Type - I made a LinkedList for that, too. And a "different" constructor for subdepartments.

• Every Company has a name.

Now I have a questions and an issue:

• QUESTION: Since a manager can be manager in only one department, I check in setManager if any department has this manager as manager. If so, then I return. Is this a correct way to do this? I thought about a boolean isManager but there's nothing like that in the specification.
• ISSUE: If I remove an Employee from a departments list with removeEmployee I set the Department variable of the Employee in the same method to null. But if I try to get the name of the Department in which the Employee is, I still get the Department and not null.

That's how the removeEmployee of the Department class code looks like:

public void removeEmployee(Employee e) {  
    employees.remove(e);  
    e.setDepartment(null);  
}

In the main method I do this to check if the Department of the Employee is null:

    departmentName.employees.remove(employeeName);
    System.out.println(employeeName.getDepartment().getName());

The Output should be null, but I get departmentName. He's removed from the employees list of the Department but to set the Department of the Employee to null fails.

I would be happy if you could answer my question and help me with my issue.

I could also upload the diagram and my three classes to let you check but I don't think you want to waste your time.

Kind regards, Newb

Answer 1

It appears that employees is some sort of List<Employee> and is public.

This makes it possible to call departmentName.employees.remove(employeeName); which does not call setDepartment(null), it would be better to declare employees as private, and only use the public removeEmployee() method to remove the employees.

This way you avoid removing employees in any other way than the way you've defined (this is called encapsulation).

Answer 2

I suggest to replace line with invoking remove method, because you don't invoke your method. Instead of that you invoke Collection method.

It should looks like this:

ObjectName.removeEmployee(employee);