Question

I have an already created Person class with its respective attributes; eventually a person can turn into an Employee.

Using inheritance, Employee can be a subclass of Person. How can you transform (“specialize”) this Person to an Employee without the need of transfering all of its attributes to the new Employee class ?

Is it better to have an independent (regarding inheritance) Employee class with an attribute of Person type (as in often seen in DB) ?

Thanks in advance!

Answer 1

This is not possible in Java. An object has a type, and can’t acquire a new one. If it’s a Person it will always be a Person, and will never be an employee. You can create a new object, of type Employee, from a Person, though :

public class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    /**
     * copy constructor
     */
    protected Person(Person p) {
        this.name = p.name;
    }

    // ...
}

public class Employee extends Person {
    private String badge;

    public Employee(Person p, String badge) {
        super(p);
        this.badge = badge;
    }

    // ...
}