its update methods inform any moved bstentry objects of their new positions we also use several simple auxiliary methods for accessing and testing datasuch as checkkeywhich checks if key is valid (albeit using fairly simple rule in this casewe also use an instance variableactionposwhich stores the position where the most recent searchinsertionor removal ended this instance variable is not necessary to the implementation of binary search treebut is useful to classes that will extend binarysearchtree (see code fragments and to identify the position where the previous searchinsertionor removal has taken place position action pos has the intended meaning provided it is used right after executing the method findinsertor remove code fragment class binarysearchtree (continues in code fragment