My advance method is not working, I need help rewriting it

$/**$

$*$ Move forward, so that the current element is now the next element in

$*$ this sequence.

$*$ @param $-$ none

$*$ @precondition

$*$ isCurrent$()$ returns true.

$*$ @postcondition

$*$ If the current element was already the end element of this sequence

$*($with nothing after it$),$ then there is no longer any current element.

$*$ Otherwise, the new element is the element immediately after the

$*$ original current element.

$*$ @exception IllegalStateException

$*$ Indicates that there is no current element, so

$*$ advance may not be called.

$**/$

public void advance$()$

$\{$

assert wellFormed$()$ : "invariant wrong at start of advance$()"$;

if$(!$isCurrent$())\{$

throw new IllegalStateException$("$No current element to Advance"$)$;

$\}$

precursor $=$ cursor;

cursor $=$ cursor.next;

$//$ TODO: Implemented by student.

assert wellFormed$()$ : "invariant wrong at end of advance$()"$;

$\}$