🚀 go-pugleaf

In the very interesting article <366732FB.D0235A7F@interlog.com>, 
shahidj@interlog.com made this clever claim...
> Okay I did that but have a look at what exactly I did.  I am writing a
> function pop().  I am not using Stacks or Vectors, I am using linked
> lists.  Basically I have wrote the methods that are used by Stack.
> 
> Here it is:
> 
> Hello,
> 
>     I have done the following
> 
>   public Object pop() throws EmptyStackException {
>   holdings = tempo.data;
>        if (top.get_next() == null) {
>            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?
> 
> Thanks
> Shahid
> 
> 
> 
> Steve Schafer (TeamB) wrote:
> 
> > On Thu, 03 Dec 1998 12:54:00 -0800, Shahid Juma <shahidj@interlog.com>
> > wrote:
> >
> > >    How do you throw an exception such as EmptyStackException?  Do you
> > >do something like this:
> > >
> > >public Object test (Object d) throws EmptyStackException {
> > >}
> > >
> > >I tried that and it doesn't do it.
> >
> > That declaration tells the compiler that the test method is _capable_
> > of throwing an exception. To actually throw the exception somewhere
> > within the body of the method:
> >
> >  throw new EmptyStackException();
> >
> > -Steve
> 
> 
> 
> 
It seems to me that you object top throws a NullPointerException instead 
of returning null when there's nothing to return. (I believe this to be 
quite common)
Try catching that instead of checking for null-refs.
Peter