binary tree this interfaces extends positionthus inheriting method elementand has additional methods for setting the element stored at the node (setelementand for setting and returning the left child (setleft and getleft)right child (setright and getright)and parent (setparent and getparentof the node class btnode (code fragment implements interface btposition by an object with fields elementleftrightand parentwhichfor node vreference the element at vthe left child of vthe right child of vand the parent of vrespectively code fragment auxiliary class btnode for implementing binary tree nodes