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  1. JDK
  2. JDK-8271164

transition to intrinsic-based range checks in java.util

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    Details

    • Type: Enhancement
    • Status: New
    • Priority: P4
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: core-libs
    • Labels:
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      Description

      There is a lot of noisy code in classes like `AbstractList` and `ArrayList` which performed index checking the 1990's way. As a cleanup, it should be refactored to use `Objects.checkFromIndexSize` and its two brothers, or even the corresponding methods in `jdk.internal.util.Preconditions`.

      There would be at least two benefits:

      1. The JIT would pay more attention to optimizing the checks.

      2. Ad hoc exception detection formatting code could be reduced.

      Example:

      ```
      --- a/src/java.base/share/classes/java/util/ArrayList.java
      +++ b/src/java.base/share/classes/java/util/ArrayList.java
      @@ -751,16 +751,24 @@ public class ArrayList<E> extends AbstractList<E>
            * A version of rangeCheck used by add and addAll.
            */
           private void rangeCheckForAdd(int index) {
      - if (index > size || index < 0)
      - throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
      + //Objects.checkFromIndexSize(index, 0, size); // 0 means index==size is OK
      + // Error message: "Range [$index, $index + 0) out of bounds for length $size"
      + //Objects.checkFromToIndex(index, index, size); // this also works, but is harder on JIT
      + // Suboptimal message customizable via the internal Preconditions API.
      + jdk.internal.util.
      + Preconditions.checkFromIndexSize(index, 0, size, ArrayList::outOfBoundsMsg4jiuP);
           }
       
           /**
            * Constructs an IndexOutOfBoundsException detail message.
            * Of the many possible refactorings of the error handling code,
            * this "outlining" performs best with both server and client VMs.
      + * FIXME: This formatting logic is duplicated at least five times
      + * in this package. Share it as a package-private method in
      + * somewhere like AbstractList or Objects.
            */
      - private String outOfBoundsMsg(int index) {
      + private String outOfBoundsMsg4jiuP(String ignore, List<Number> indexZeroSize) {
      + Number index = indexZeroSize.get(0), size = indexZeroSize.get(2);
               return "Index: "+index+", Size: "+size;
           }
       
      ```

      The above example is chosen to show how an *inclusive* range check may be done. The error message can be adjusted in the way shown.

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              Assignee:
              Unassigned Unassigned
              Reporter:
              jrose John Rose
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                Dates

                Created:
                Updated: