Question about declaring variables

Hi guys,

I have a basic question about declaring variables. I've read that when declaring a set, for instance, one wants to begin with the most basic declaration followed by something more specific, like so:

Set<String> my_set = new HashSet<String>();

Why is this better than doing the following:

HashSet<String> my_set = new HashSet<String>();

It seems like a trifle, and it may be, but I still don't understand the advantages of the first case.

Imagine a third party software vendor made a hash set that was far more efficient than the one you have. You could just swap it in like this:

import org.betterSofware.utilities.*

Set<String> my_set = new BetterHashSet<String>();

But if you had this..

HashSet<String> my_set = new HashSet<String>();

you would have to trawl through your code base to see where people had used my_set as a HashSet, e.g

HashSet<String> my_other_set = my_set;

because swapping in a BetterHashSet would invalidate such code, wherever it appeared.

Got it, thanks 2by4!