JAVA - about ArrayList

Question

Hi i have a question about ArrayList in Java.

I have in a class called "Utente" an ArrayList ricFriends; Now, the problem is that i have a method called

requestFriendship(Utente u) 

where i want to add in the u.ricFriends the object Utente that call the method...

I tried in this way but it's at 99% wrong..

public void requestFriendship(Utente u){
 u.ricFriends.add(this);
}

for example i want to do this :

Utente Gary = new Utente();
Utente Mike = new Utente();
Gary.requestFriendship(Mike);

And if i check Mike.ricFriends i can see the object Gary;

Sorry for the english, thank you.

• laune: According your description, requestFriendship works correctly: the object for which you call this method is added to the list owned by the Utente parameter.
• slartidan: What exactly is your question?
• Andrew Aitken: That looks like it should work, what is wrong with it?
• kamaci: It should add Gary to Mike and seems working. Do you want to add Mike to Gary too?
• Edoardo Maurizio: Sorry, i solved, it works

Answer 1

Not sure what you're trying to do, but you should change this line:

 u.ricFriends.add(this);

for this:

 this.ricFriends.add(u)

Answer 2

First of all, you are making a attribute public, that's not a good practice in OO programming, you should create get and set methods.

About you problem, you could do it something like this:

ArrayList<Utente> utenteList = u.getRicFriends();
utenteList.add(Mike);

Take care about "this" pointer, "this" mean that you are taking the object reference himself.

• slartidan: Returning mutable lists is also often seen as bad practice in OO programming. I would prefer an addRicFriend(Mike) method. This would make changes in u easier - the internal detail, whether ricFriends is an Array, an ArrayList or anything else is encapsulated.