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  1. JDK
  2. JDK-8267359

Stream.flatMap() consumes entire flatmapped stream when Stream.iterator() is called

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Details

    • Bug
    • Status: Resolved
    • P4
    • Resolution: Won't Fix
    • 11.0.9.1, 16, 17
    • None
    • core-libs

    Description

      Following up on https://bugs.openjdk.java.net/browse/JDK-8075939, there's still a case where Stream.flatMap() doesn't get short circuited, when using Stream.iterator():

      // --------------------------------------------------------
      Iterator<Integer> it =
          Stream.of("a", "b")
              .flatMap(s -> Stream
                  .of(1, 2, 3, 4)
                  .filter(i -> { System.out.println(i); return true; }))
              .iterator();

      it.hasNext(); // This consumes the entire flatmapped stream
      it.next();
      // --------------------------------------------------------

      The above program prints:

      1
      2
      3
      4

      This program never stops:

      // --------------------------------------------------------
      Iterator<Integer> it =
          Stream.of("a", "b")
              .flatMap(s -> Stream
                  .iterate(1, i -> i)
                  .filter(i -> { System.out.println(i); return true; }))
              .iterator();

      it.hasNext();
      it.next();
      // --------------------------------------------------------

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              psandoz Paul Sandoz
              leder Lukas Eder
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                Created:
                Updated:
                Resolved: