Details

    • Type: Bug
    • Status: Closed
    • Priority: Major
    • Resolution: Won't Fix
    • Affects Version/s: 3.2.1
    • Fix Version/s: None
    • Component/s: None
    • Labels:
      None
    • Environment:

      java 1.6.0_24
      Ubuntu 11.10

      Description

      Hi,

      I am encountering a performance problem in ListUtils.removeAll(). It
      appears in version 3.2.1 and also in revision 1355448. I attached a
      test that exposes this problem and a one-line patch that fixes it. On
      my machine, for this test, the patch provides a 217X speedup.

      To run the test, just do:

      $ java Test

      The output for the un-patched version is:
      Time is 5430

      The output for the patched version is:
      Time is 25

      As the patch shows, the problem is that
      "ListUtils.removeAll(Collection<E> collection, Collection<?> remove)"
      performs "remove.contains(obj)" for each element in "collection",
      which can be very expensive if "remove.contains(obj)" is expensive,
      e.g., when "remove" is a list.

      The one-line patch I attached puts the elements of "remove" in a
      HashSet (which has very fast "contains()"), if "remove" is not already
      a set:

      "if (!(remove instanceof java.util.Set<?>)) remove = new HashSet<Object>(remove);"

      Is this a bug, or am I misunderstanding the intended behavior? If so,
      can you please confirm that the patch is correct?

      Thanks,

      Adrian

        Attachments

        1. patch.diff
          0.7 kB
          Adrian Nistor
        2. Test.java
          0.7 kB
          Adrian Nistor

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            • Assignee:
              Unassigned
              Reporter:
              adriannistor Adrian Nistor
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              Dates

              • Created:
                Updated:
                Resolved: