How to compute the hash code for a stream in the same way as List.hashCode()

Question

I just realized that implementing the following algorithm to compute the hash code for a stream is not possible using Stream.reduce(...). The problem is that the initial see

Answer 1

The easiest and shortest way I found was to implement a Collector using Collectors.reducing:

/**
 * Creates a new Collector that collects the hash code of the elements.
 * @param  the type of the input elements
 * @return the hash code
 * @see Arrays#hashCode(java.lang.Object[])
 * @see AbstractList#hashCode()
 */
public static  Collector toHashCode() {
    return Collectors.reducing(1, Objects::hashCode, (i, j) -> 31 *  i + j);
}

@Test
public void testHashCode() {
    List list = Arrays.asList(Math.PI, 42, "stackoverflow.com");
    int expected = list.hashCode();
    int actual = list.stream().collect(StreamUtils.toHashCode());
    assertEquals(expected, actual);
}