$\frac{?}{?}****$

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

this sequence.

eparam $-$ none

eprecondition

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 current element is the element immediately after the

original current element.

@exception IllegalStateException

If there was no current element, so

advance may not be called $($the precondition was false$).$

$**$I

public void advance$()$

$\{$

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

$//$ TODO: Implement this code.

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

$\}$

Can help me to complete todo