code: private void pushState(Node<K,V>[] t, int i, int n) {
              TableStack<K,V> s = spare;  // reuse if possible
              if (s != null)
                  spare = s.next;
              else
                  s = new TableStack<K,V>();
              s.tab = t;
              s.length = n;
              s.index = i;
              s.next = stack;
              stack = s;
          }
docs: Saves traversal state upon encountering a forwarding node.