You can do all the required work without any data structure.

But then you have to handle all the issues like variable
size of array, synchronization etc, by yourself.

If you think you have got time as well as skills to

do this things in a better manner, you are always welcome
but if you think that you should use your time
in developing the application logic, leave this routine as well
as complex work for the experts. This is what

data structures are all about.

well, Vectors make more sense in a if u'r into a situation where more than one thread modifies your collection at the same time, cuz vectors are essentially synchronized...ArrayLists and the rest aren't ! so essentially u end up working up with an overhead
of course there are APIs wherein u cud integrate these Legacy APIs with your collections framework...