Simple problem with a list initialization.

Question

hello ! i have a class Contact and i would like to make a list of lists of Contact variables .. but when i try to run my code , it says "IndexOutOfBoundsException: Index: 0, Size: 0" . I know that every list of the list must be initialized .. but i don't know how .
here is the declaration of the List
static  List<List<Contact>> lolContact=new ArrayList<List<Contact>>();and i know that i should do something like :
lolContact.get(0)=new ArrayList<Contact>();to initialize every list of the list but i don't know how . please help

Answer 1

badescuga wrote:
and i know that i should do something like :
lolContact.get(0)=new ArrayList<Contact>();
Couple of problems with that.
1. You can never do methodCall() = something in Java. The result of a method call is not an L-value.
2. You're trying to assign a ContactList to a Contact variable. Basically, you're trying to do
Contact c = new ArrayList<Contact>();3. Even if you changed it to
Contact c = lolContact.get(0);
c = new Contact();it would not put anything into the list. That would just copy the first reference in the list and stick it into variable c, so that both c and the first list item point to the same object (remember, the list contains references, not objects--no object or data structure ever contains an object in Java), and then assigns a completely different reference to c, forgetting about the one to the object pointed to by the list. It would not affect the list in any way.
4. You can't do get(0) until you've first put something into the list.