Re: Amazing: Vector can have elements of different types!!!
Shawn wrote:
I just realized/found that in Java, Vector can have elements with
different types. I guess other collections are the same. See my code
below. I don't know Generics from Java 5.0. But I am really amazed that
heterogenous types of data can be put in the same place(Vector).
I have a couple questions:
(1)Is that common that people utilize this feature (putting different
types of data in one place)?
Yes, very common. There are good reasons to do it (which is common) and there
are bad reasons to do it (which I hope and trust is rare). The good reasons
are when all the objects have /something/ in common -- for instance they could
all implement some specific interface, or they could share a common
(non-trivial) base class. In that case the code using the collection doesn't
care what kinds of objects they are /except/ that they have the common
property. You could say that from that code's point-of-view the collection
/isn't/ heterogeneous -- they are all the exactly same kind of thing in the
only sense it cares about.
So you end up with code like (for example):
Interface fireable { void fire(); }
List = // ... some list
for (Iterator it = list.iterator(); it.hasNext(); )
{
Fireable f = (Fireable)it.next();
f.fire();
}
Generics, in 1.5, are an attempt to formalise this sort of pattern.
However there are also bad reasons for creating heterogeneous lists. A
reasonable (but certainly not 100% reliable) rule-of--thumb is that you are
going wrong if you ever need an answer to:
(2)Is there a way to find out what type of each element belongs to? (say
I forgot 1st element is Person, 2nd element is String, etc)
-- chris