CODEWITHSUNDEEP
javapointersserialization
Marco Merlini
Marco Merlini

Reputation: 955

Redundant serialization of linked list and pointer into list

I have kind of a contrived question.

Let's say I have a linked list of users, and one of these users is "User of the week":

public class UserOfTheWeek implements Serializable {
    private UserNode root;
    private UserNode userOfTheWeek;

    //...

    private class UserNode {
        String username;
        UserNode next;
    }

    public void saveToFile() {
        ObjectOutputStream oos = new ...
        oos.writeObject(root);
        oos.writeObject(userOfTheWeek);
    }
}

root obviously stores a reference to the head of the list, and userOfTheWeek could point to any of the nodes. I want to save the linked list, but will saving the userOfTheWeek make a copy of a part of the list? If the user at the head of the list happens to be the user of the week, this could save the entire list twice, and worse, userOfTheWeek wouldn't point to an object in the list pointed at by root.

Does anyone know what will happen? And if not, I am also open to an alternate solution.

Upvotes: 0

Views: 45

Answers (1)

user207421
user207421

Reputation: 310876

I want to save the linked list, but will saving the userOfTheWeek make a copy of a part of the list?

No.

If the user at the head of the list happens to be the user of the week, this could save the entire list twice

No.

The stream knows which objects have already been serialized to it, and doesn't reserialize them. See the Object Serialization Specification #1.2. Similarly, the object is only deserialized once. Object graphs can be serialized and recovered in full generality, including cycles.

and worse, userOfTheWeek wouldn't point to an object in the list pointed at by root.

You would have to serialize and deserialize that separately, but it won't result in creation of a new object, it will refer to an object in the list.

Upvotes: 1

Related Questions