🚀 go-pugleaf

Shahid Juma wrote:

>   public Object pop() throws EmptyStackException {
>   holdings = tempo.data;
>        if (top.get_next() == null) {     <<<--------- PROBLEM HERE
>            top = null;
>            tempo = null;
>            temp = null;
>        throw new EmptyStackException();
>        }
>
>   else {
>            tempo = tempo.get_next();
>            top.set_next(null);
>            top = tempo;
>     }
>        return holdings;
>
>    }
>
>  This doen't seem to work, it says the following:
>
> java.lang.NullPointerException
>         at LinkedStack.pop(Compiled Code)
>         at LinkedStack.pop(Compiled Code)
>         at Assignment4.interactiveTest(Compiled Code)
>         at Assignment4.main(Assignment4.java:31)
>
> Is anything wrong anywhere?

If your stack is empty, then TOP = NULL.  However, your code never checks
whether TOP is NULL or not -- instead, it immediately looks at TOP.GET_NEXT()
which will always cause a NullPointerException if the stack is empty.