Re: Yet Another ClassCastException Question

From:
"Mike Schilling" <mscottschilling@hotmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 01 May 2006 19:51:20 GMT
Message-ID:
<YEt5g.10528$Lm5.3305@newssvr12.news.prodigy.com>
"Timo Stamm" <timo.stamm@arcor.de> wrote in message
news:445653c3$0$11079$9b4e6d93@newsread4.arcor-online.net...

Bjorn Abelli schrieb:

"Oliver Wong" wrote...

I thought to myself "But what if I then try to put a String into oad?"
So I tried it out, and I got a runtime ArrayStoreException. To me, this
looks
like a pretty ugly language design.


Well, I think it's actually better with that "stricter" typesafety than
the similar construction with "generic" collections. I tested the
following snippet in 1.6:

   ArrayList old = new ArrayList<Date>();

   old.add("foo");


This is not a valid comparison. The compiler warns you about the usage of
the raw type in the above code. A valid complement to

  Object[] oad = new Date[];

is

  ArrayList<Object> old = new ArrayList<Date>();

and this gives you an error.


Generics work differently than arrays, and this is going to cause confusion
now and for the rest of Java's lifetime.

    Date[] dad = newDate[12]
    Object[] oad = dad;

is perfectly safe, because

    oad[1] = new Object();

will cause an ArrayStoreException then and there. No data structures will
be corrupted and no subtle bugs introduced.

On the other hand

    ArrayList<Date> dal = new ArrayList<Date>();
    ArrayList<Object> oal = (ArrayList<Object>)dal;

is unsafe, because

    oal.add(new Object());

will succeed, and only at some later time will

    Date d = dal.get(12);

throw an exception, making it clear that there's been a problem *somewhere*.

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