Question

Would the below be correct for the following statement. “A man has a best friend who is a dog.”

public class Mann {
     private BestFriend dog;
     //etc
}

Answer 1

Looks like Dog should by type, because man can have other “type of best friend”:

public class Mann {
     private Dog bestFriend;
     //etc
}

Update

Most close to real-live implementation will look like:

public interface Friend {}

public class Man implements Friend {}

public class Dog implements Friend {}

public class FriendRelationship {
    private Friend first;
    private Friend second;

    public FriendRelationship(Friend first, Friend second) {
        this.first = first;
        this.second = second;
    }
}

Man aPerson = new Man();
Dog aBog = new Dog();
FriendRelationship bestFriends = new FriendRelationship(aPerson, aDog);

This way one can express friend relationships between any entities. Common base class is not required. You only need implement Friend interface.