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Asked: 2026-05-20T01:42:20+00:00

I need to store a growing large number of objects in a collection. While

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I need to store a growing large number of objects in a collection. While performing actions of each object of the collection, I regularly need to check whether an object is already stored. If an object is not stored yet I will add it to the end of the collection. I process each object iteratively while doing the checks.

Objects already processed should not be removed from the collection because I do not want put them back to processing when I stumble upon them again.

As a result I do not know what collection may fit best. HashSet has a constant time “contains” method but a List has faster methods to iterate over its elements, right ?

What would be the wiser choice ? Would it be relevant to keep two different structures at a time containing the same nodes, a HashSet for the checks and a LinkedList for the processing ?

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1 Answer

  1. Editorial Team

    1) Use ArrayList, not LinkedList. LinkedLists consume a lot of memory, and it’s slower on iteration than ArrayList.

    2) I’d suggest to use two data structures. E.g. for the sake of you being unable to add to a collection wile iterating through it (ConcurrentModificationException)

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