Creating Objects exclusively with Factory

Question

I'm currently working on a student project and wondering if there is a way to create objects exclusively with factory methods?

public class PersonFactory {

    public static Person createPerson() {
        // some constraints ...
        return new Person();
    }

}

My exemplary PersonFactory.java is supposed to return Person objects with its createPerson() method.

public class Person {

    // some examples ...
    private String name;
    private int age;

    public Person() {
        // ...
    }

}

This works fine, but in the main program, I am still able to create Person objects with their common constructor (since it is public). But if I change the constructor to private, the factory method cannot access it either.

public class PersonManagement {

    public static void main(String[] args) {
        // both still works ...
        Person p1 = new Person();
        Person p2 = PersonFactory.createPerson();
    }

}

Thank you so much in advance ;)

Answer 1

You can make the Person constructor package private (i.e. remove the public access modifier), which will only allow classes from the same package to access it.

Then, if PersonFactory belongs to the same package as Person, it would have access to that constructor.

If PersonManagement belongs to a different package, it won't have access to that constructor.

Another option is to keep the Person constructor private and move the createPerson() method to the Person class.

Answer 2

I usually solve the problem by putting the factory method in the Person class rather than in a separate factory class. In this case the constructor can be private, and Person objects can be obtained from the factory method and nowhere else. Don’t know whether that could fit into your design, though.

One potential issue here would be if you didn’t want your factory method static. However, I see that yours is, so this shouldn’t stop you.