Re: imcompatible type when converting a List to array

From:

Nigel Wade <nmw@ion.le.ac.uk>

Newsgroups:

comp.lang.java.help

Date:

Thu, 19 Jun 2008 16:48:33 +0100

Message-ID:

<g3dv4i$l0d$1@south.jnrs.ja.net>

thufir wrote:

I have an ArrayList<Guest> which I want to convert to an Array, but I'm
getting:

init:
deps-jar:
Compiling 2 source files to /home/thufir/JavaProject28/build/classes
/home/thufir/bcit-comp2611-project2/src/a00720398/view/Tabs.java:15:
incompatible types
found : java.lang.Object[]
required: a00720398.data.Guest[]
Guest some_guests[] = FileUtil.getGuests().toArray();
1 error
BUILD FAILED (total time: 6 seconds)

If I change it to:

Object some_guests[] = FileUtil.getGuests().toArray();

then it works fine, but that's rather absurd because I know that the type
is Guest so I don't see why it would have to be an array of Object.

Surely I don't have to cast to Guest?

thanks,

Thufir

There's another method which does what you want. It's a bit of a "hack", but it
does allow you to get an array of the correct type.

ArrayList implements Collection, and Collection has two toArray() methods. The
second method:
<T> T[] toArray(T[] a);
allows you to pass an array of type T as parameter, and it will return an array
of the same type. If the array passed is large enough it will put the contents
into that array, otherwise it creates a new array sufficient to hold the
contents. The "hack" is to pass an array of size 0:

Guest some_guests[] = FileUtil.getGuests().toArray(new Guest[0]);

--
Nigel Wade