I have a web service that holds information for users. Each user has a list of items, possibly thousands. I want to add an item to the list without loading the entire list. Is there a list implementation that allows you to add elements to the list without bringing the entire list into memory?
A:
None that I know. With middlewares such as Terracotta, some collections (such as maps) can be loaded on-demand and partially, but this doesn't exist as-is in the standart JDK.
Olivier Croisier
2010-03-11 15:45:42
+1
A:
A Doubly Linked List. By definition it's not necessary to traverse the list to add something to the end since it contains a pointer to the end.
Amber Shah
2010-03-11 15:47:12
After reading the other answer, I think maybe I was being too abstract in my answer. On the other hand, maybe that's what you wanted...
Amber Shah
2010-03-11 15:48:19
He asked about the memory footprint, not about the speed. Any and all in-memory list are, well.. in-memory..
arcticpenguin
2010-03-11 15:50:14
Yes, all in memory lists are ... in memory. You are right.What I was saying was, if you have a not-in-memory list (in a file, in a DB, don't care, etc) then the way to add to the end would be to have a "pointer" to the end. When I said it's not necessary to traverse the list, I didn't mean you'd save time, I meant you don't need those items in memory.
Amber Shah
2010-03-11 17:25:44
+1
A:
the list is on a remote database. – Lumpy
So the list is in a database, so it's not really a Java List? It's just a bunch of database rows? In that case why not just do an insert into the database to add another row?
mbaird
2010-03-11 15:57:44
+1
A:
Lazy proxies. You can use a JDK dynamic proxy (java.lang.reflect.Proxy) where you store only the information needed for retrieving the items from the database, not the items themselves. Only when calling the get(..), size(), contains(..) methods - fetch the data.
However I have a feeling that you are doing things the wrong way. Give more details about your implementation.
Bozho
2010-03-11 16:01:45