static void arraycopy(O[] a, O[] b) {
  if (a != null && b != null)
    arraycopy(a, 0, b, 0, min(a.length, b.length));
}

static void arraycopy(O src, int srcPos, O dest, int destPos, int n) {
  System.arraycopy(src, srcPos, dest, destPos, n);
}