Java Confused with potential is a and is involved in a relationship.

[Hilton D]

I'm attempting to set up a new database architecture now that we've opted to use Hibernate. Previously, I had the three classes shown below in my Java code.
Super Class:

public abstract class Card {
    
    private String firstname;
    private String lastname;
    private String email;
    ...
}

And a few more to come. This seems to function properly. However, I am beginning to become perplexed. The subclasses in are relationships, and some card is a card. However, I am unable to translate this into database tables.
A card sub class:

public class ContactCard extends Card{
    private String variable1;
    private String variable2;
    private String variable3;

    public ContactCard(){

        super(firstname, lastname, email);
        ...
    }
}

To include the procedure of a card table in the database, for example, I could create a table for each subclass type, and inside this table, I could have an id that refers a card table (which is generated when a user registers). But does this indicate that I've changed the is a relationship in my database to has a? (as done in this example) The subclass now has a card instead of being a card.
I'm perplexed and hoping that someone can help me understand.
Thanks