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.

According your description, requestFriendship works correctly: the object for which you call this method is added to the list owned by the Utente parameter. — laune
– laune, Commented Apr 11, 2016 at 16:08
It should add Gary to Mike and seems working. Do you want to add Mike to Gary too? — kamaci
– kamaci, Commented Apr 11, 2016 at 16:09

raven · Accepted Answer · 2016-04-11 16:09:06Z

2

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

 u.ricFriends.add(this);

for this:

  this.ricFriends.add(u)

answered Apr 11, 2016 at 16:09

raven

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Comments

Ricardo Romero Benítez · Accepted Answer · 2016-04-11 16:17:44Z

0

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.

answered Apr 11, 2016 at 16:17

Ricardo Romero Benítez

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1 Comment

slartidan Over a year ago

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.

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