/**
* Constructs a rose tree branch.
*
* @param value A value.
* @param children A non-empty list of children.
* @throws NullPointerException if children is null
* @throws IllegalArgumentException if children is empty
*/
public Node(T value, List<Node<T>> children) {
Objects.requireNonNull(children, "children is null");
this.value = value;
this.children = children;
this.size = Lazy.of(() -> 1 + children.foldLeft(0, (acc, child) -> acc + child.length()));
this.hashCode = 31 * 31 + 31 * Objects.hashCode(value) + Objects.hashCode(children);
}
private static int testHashCode() {
int errors = 0;
errors += (Objects.hashCode(null) == 0) ? 0 : 1;
String s = "42";
errors += (Objects.hashCode(s) == s.hashCode()) ? 0 : 1;
return errors;
}