Saving an object that contains a list of objects to the disk

Question

The title may be a little be confusing or even missleading but im trying to save to disk an object that as a property contains a list of objects (ArrayList).

The thing is this object wont be able to do anything without the list.

I have tried serialization of both the object and the list. When i tried serializing the object alone there was nothing in it, the list was empty. When i tried serializing the list i could access the list, change it but at the cost of many thrown exceptions.

public class AdressBook implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 6399534374362987383L;

    static Reader reader = new KeyboardReader();

    static ArrayList<Contact> AdressBook = new ArrayList<Contact>();

    public AdressBook(){

    }

    public static void AddContact(){
        AdressBook.add(new Contact());
    }

    public static void EditContact(){
        System.out.println("Which contact you desire to edit?");
        Libreta.Display();
        System.out.println("Type in the number of the contact.");
        int i = (reader.readint() - 1);

        System.out.println("Choose the change 1.Name 2.Last Name 3.Nickname 4.Phone number 5.Emails");
        int j = reader.readint();

               switch(j){

        case 1: AdressBook.get(i).setName();
                break;

        case 2: AdressBook.get(i).setLastName();
                break;

        case 3: AdressBook.get(i).setNick();
                break;

        case 4: AdressBook.get(i).AddPhoneNumber();
                break;

        case 5: AdressBook.get(i).AddEmail();
                break;

        default : System.out.println("Not a valid option");

        }

I have to be able to edit the list of the object and being able to somehow save it again. I have been trying many ways but im lacking in knowledge or it just doesnt work for me.

Look at [How to Serialize a list in java?](http://stackoverflow.com/questions/1387954/how-to-serialize-a-list-in-java) — Braj, Apr 15 '14 at 20:25

score 0 · Accepted Answer · answered Apr 15 '14 at 20:33

Your address book variable should not be declared static, as static variables are not serialized. Make it an instance (non-static) variable like this:

public class AddressBook implements Serializable {
...
  ArrayList<Contact> contacts = new ArrayList<Contact>();
...
}

score 0 · Answer 2 · answered Apr 15 '14 at 20:38

I think your problem is that your ArrayList is a static field (sometimes called a class field) and serialization take place in an object instance not in class.

So you should replace your static field, and static methods too, for instance equivalents.

(Now, just a comment: you should try using java naming conventions - using lower initials for field and method names - it much easy for java coders understand you... ;-)

Saving an object that contains a list of objects to the disk

2 Answers2