Java random insert collection

Question

I am considering using a Java collection that would work best with random insertions. I will be inserting a lot and only read the collection once at the end.

My desired functionality is adding an element at a specified index, anywhere between <0, current_length>. Which collection would be the most efficient to use?

Java. The collection will grow and the indexes would be in range 0-length — Bober02, Jun 10 '12 at 17:29
OK, I modified the question. I want to use some collection like ArrayList, which exposes add(Eleem, index) method, that would be most efficient on insertions. Thanks — Bober02, Jun 10 '12 at 17:43
What is your usecase? Is it possible to change algorithm to avoid random insertions e.g. by inserting sequentially and then shuffling once? — , Jun 10 '12 at 17:45
No, the values must be inserted at a specific place as I go along — Bober02, Jun 10 '12 at 18:22

score 0 · Accepted Answer · answered Jun 10 '12 at 18:00

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Useful link for your reference: http://www.coderfriendly.com/wp-content/uploads/2009/05/java_collections_v2.pdf

Not entirely sure how you will be reading the information post input (and how important it is to you). Hashmap or ArrayList would make sense depending on what you are looking to do. Also not sure if you are looking for something thread safe or not. Hope it helps.

answered Jun 10 '12 at 18:00

ali haider

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what?? Random insertions into an ArrayList? – unbeli Jun 10 '12 at 20:42
@unbeli - I may have misunderstood the question but I do not think that you understood it clearly as well. – ali haider Jun 10 '12 at 23:52

score -2 · Answer 2 · edited May 23 '17 at 12:21

The inefficiency of using List is endemic to the problem. Every time you add something, every subsequent element will have to be re-indexed - as the javadoc states:

Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

From your question/comments, it would appear that you have a bunch of Objects, and you're sorting them as you go. I'd suggest a more efficient solution to this problem would be to write a Comparator (or make your object implement Comparable), and then use Collections.sort(list, comparator) (or Collections.sort(list)).

You might suggest that your Objects are being sorted on the basis of other variables. In which case, you could create an extension of the Object, with those other variables as fields and extending Comparable, and with a method like getOriginal(). You add these wrapped objects to your list, sort, and then iterate through the list, adding the original objects (from getOriginal()) to a new list.

For info on the sorting algorithm of collections - see this SO question

List is an interface, it cannot be inefficienct. Inserting into LinkedList is O(1), but you need to find first. SkipList might help, but it's not in JRE. — unbeli, Jun 10 '12 at 20:54

Java random insert collection

2 Answers2