And you're posting these questions in the Back Porch, and not Developer's Den, because...?
Vector doesn't "change" anything -- it uses object as a way to have a loosely typed collection. You may want to look into "generics" to find a way to create a more strongly typed collection. Though if you're throwing several different kinds of isntances into it (which would be a bad idea anyway) that won't help.
Caveat: it's been a while since I did any Java, and I've been doing C# since, so my memory could be somewhat muddled.