android/guava/src/com/google/common/collect/Sets.java
static int hashCodeImpl(Set<?> s) {
    int hashCode = 0;
    for (Object o : s) {
      hashCode += o != null ? o.hashCode() : 0;

      hashCode = ~~hashCode;
      // Needed to deal with unusual integer overflow in GWT.
    }
    return hashCode;
  }
static int hashCodeImpl(Set<?> s) {
    int hashCode = 0;
    for (Object o : s) {
      hashCode += o != null ? o.hashCode() : 0;

      hashCode = ~~hashCode;
      // Needed to deal with unusual integer overflow in GWT.
    }
    return hashCode;
  }
An implementation for {@link Set#hashCode()}.