Overall it looks pretty good.
A few things:-
1) when you start the program the first time - if you do nothing except
select (6) quit, it errors when you open the program the next time.
Test by renaming your current "stock.txt".
this can be fixed by changing
do
{
}while (input.ready());
to
while (input.ready())
{
}
but don't know if this will break something else
2) suggest your program which look like this
to this
this way your code can be called by another program
3) when displaying the results of a query eg current stock level, after the
code to display the results, add something like this
System.out.println("Press [ENTER] to continue");
String junk = input.readLine();
this way the result will be at the bottom of the screen, where it is
expected to be, instead of near the top, with the next option menu showing
at the bottom ie you currently have to search the screen for the result.
4) if you want to have a bit of fun, try to convert it from arrays of data
to a HashMap of objects - StockItem, with the stockCode being the key
I'm away for a couple of days, and if I get a chance I'll try to rewrite it
the way I've suggested, which is probably an easier way to show you the
difference.