} else { if ($temp->next === NULL && $temp->prev != NULL) { $node->prev = $temp->prev; $node->next = $temp; $temp->prev = $node; } else { if ($temp->prev != NULL && $temp->next != NULL) { $temp->prev->next = $node; $node->prev = $temp->prev; $temp->prev = $node; $node->next = $temp; } } } } } } $node1 = new Node(3); $node2 = new Node(10); $node3 = new Node(20); $node4 = new Node(50); $node5 = new Node(99); $node6 = new Node(30); $station1 = new Station(); $station1->add_node($node1); $station1->add_node($node2); $station1->add_node($node3); $station1->add_node($node4); $station1->add_node($node5); $station1->insert_node($node6, 5); var_dump($station1);