Adding to an element in an ArrayList in Java?

Question

At the moment inside the class I have ArrayList which the objects are stored in when they are added to the club. I also have a integer which would be auto incremented once a object has been added to the ArrayList. However, I am unsure how I would be able to add the registration ID with the player object in the ArrayList.

how does your Player class look like? does Player class have a property int registrationId ? — Kent
– Kent, Commented Mar 26, 2012 at 16:52
What does your Player class look like? If I can make an assumption that Player.setRegID(int) is defined, then it would be straightforward. — nobeh
– nobeh, Commented Mar 26, 2012 at 16:53
there is no need for your model to increment the registration id by yourself. every time you add a new object into players, the arraylist size will be automatically incremented. you can get the size with players.size(); if you want to ask, which id a current player object has, call players.indexOf(player). — andreasg
– andreasg, Commented Mar 26, 2012 at 16:54
I assume Players can be part of multiple Clubs, in which case it doesn't make sense to store the registration ID in the Player class, unless the method is something like Player.setRegId(Club c, int id). — smessing
– smessing, Commented Mar 26, 2012 at 16:55
I like @andreasg's solution as an alternative to what I posted. It's clean and straightforward. The only potential issue is if Players can leave a Club, then you'll need a separate structure to keep track of Players who are no longer valid (removing them from the list would change all the ID numbers). — smessing
– smessing, Commented Mar 26, 2012 at 16:56

Eugene Kuleshov · Accepted Answer · 2012-03-26 16:54:22Z

2

It is not completely clear from your description what exactly you are trying to do, so I am guessing something like this:

public synchronized void registerPlayer(Player p)
{
    p.setRegistrationId(registrationID++);
    players.add(p);
}

answered Mar 26, 2012 at 16:54

Eugene Kuleshov

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Comments

smessing · Accepted Answer · 2012-03-26 16:53:20Z

One solution is to use a Map, which associates the individual ID with the particular player, as a key-value pair, instead of a List:

public class Club
{

    private String clubName;
    private int registrationID;
    private Map<Player, Integer> players;

    /**
     * Create a club with given club name.
     */
    public Club(String clubName)
    {
        players = new HashMap<Player, Integer>();
        this.clubName = clubName;
        registrationID = 1;
    }

    public void registerPlayer(Player p)
    {
        // check if player is already in the club:
        if (!players.containsKey(p)) {
            players.put(p, new Integer(registrationID));
            // increment ID counter:
            registrationID++;
        }
    }

    public void listAll () 
    {
        for (Player p : players.keySet()) {
            System.out.println(p);
        }
    }

}

ggrigery · Accepted Answer · 2012-03-26 16:55:07Z

0

Try creating another class:

public class Registration() {
    private Player player;
    private String registrationId;

    public Registration(Player p) {
        // Assign p to player
        // Generate the registration ID
    }
}

Then just have ArrayList<Registration> registrations to hold all these. Your listAll() method would then need to reference i.getNext().getPlayer() to perform the same action.

answered Mar 26, 2012 at 16:55

ggrigery

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Comments

keyser · Accepted Answer · 2012-03-26 16:56:29Z

0

I'm guessing Player has a field for ID which you want to set after adding it to the arraylist?

If you know the index of the Player, just fetch the object with the get method and set the ID. If you don't have the index, you'll have to loop through the arraylist to find your object.

answered Mar 26, 2012 at 16:56

keyser

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