/**
   * Returns a {@code Collector} that returns the {@code k} greatest (relative to the specified
   * {@code Comparator}) input elements, in descending order, as an unmodifiable {@code List}. Ties
   * are broken arbitrarily.
   *
   * <p>For example:
   *
   * {@snippet :
   * Stream.of("foo", "quux", "banana", "elephant")
   *     .collect(greatest(2, comparingInt(String::length)))
   * // returns {"elephant", "banana"}

      assertTrue(t.equals(t));

      for (int j = i + 1; j < valuesInExpectedOrder.size(); j++) {
        T greater = valuesInExpectedOrder.get(j);
        assertTrue(greater + ".compareTo(" + t + ')', greater.compareTo(t) > 0);
        assertFalse(greater.equals(t));
      }
    }
  }

  /**
   * Returns a collection that simulates concurrent modification by having its size method return

   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated; use the
   * equivalent {@link Integer#compareUnsigned(int, int)} method instead.
   *
   * @param a the first unsigned {@code int} to compare
   * @param b the second unsigned {@code int} to compare
   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
   *     greater than {@code b}; or zero if they are equal
   */

   */
  public double populationCovariance() {
    checkState(count() != 0);
    return sumOfProductsOfDeltas / count();
  }

  /**
   * Returns the sample covariance of the values. The count must be greater than one.
   *
   * <p>This is not guaranteed to return zero when the dataset consists of the same pair of values
   * multiple times, due to numerical errors.
   *
   * <h3>Non-finite values</h3>
   *

   */
  public double populationCovariance() {
    checkState(count() != 0);
    return sumOfProductsOfDeltas / count();
  }

  /**
   * Returns the sample covariance of the values. The count must be greater than one.
   *
   * <p>This is not guaranteed to return zero when the dataset consists of the same pair of values
   * multiple times, due to numerical errors.
   *
   * <h3>Non-finite values</h3>
   *

    IndexOutOfBoundsException expected =
        assertThrows(IndexOutOfBoundsException.class, () -> checkPositionIndex(2, 1));
    assertThat(expected).hasMessageThat().isEqualTo("index (2) must not be greater than size (1)");
  }

  public void testCheckPositionIndex_withDesc_negative() {
    IndexOutOfBoundsException expected =
        assertThrows(IndexOutOfBoundsException.class, () -> checkPositionIndex(-1, 1, "foo"));

    IndexOutOfBoundsException expected =
        assertThrows(IndexOutOfBoundsException.class, () -> checkPositionIndex(2, 1));
    assertThat(expected).hasMessageThat().isEqualTo("index (2) must not be greater than size (1)");
  }

  public void testCheckPositionIndex_withDesc_negative() {
    IndexOutOfBoundsException expected =
        assertThrows(IndexOutOfBoundsException.class, () -> checkPositionIndex(-1, 1, "foo"));

   * greater than or equal to that.
   */
  private static int partition(double[] array, int from, int to) {
    // Select a pivot, and move it to the start of the slice i.e. to index from.
    movePivotToStartOfSlice(array, from, to);
    double pivot = array[from];

    // Move all elements with indexes in (from, to] which are greater than the pivot to the end of

          return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
        }

        @Override
        public int result() {
          return 0;
        }
      };

  private static final ComparisonChain LESS = new InactiveComparisonChain(-1);

  private static final ComparisonChain GREATER = new InactiveComparisonChain(1);

constraints.DecimalMin.message = {item} must be greater than {value}.
constraints.Digits.message = {item} must be a number. (expected: <number>.<number>)
constraints.Future.message = {item} must be a future value.
constraints.Max.message = {item} must be less than or equal to {value}.
constraints.Min.message = {item} must be greater than or equal to {value}.
constraints.NotNull.message = {item} is required.