Re: Why is this assertion being triggered?

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 09 Jan 2007 00:29:03 GMT

Message-ID:

<jlBoh.8885$w91.6236@newsread1.news.pas.earthlink.net>

thebad1 wrote:

Hi,

I have a strange error, that I can reproduce using jre1.5.0_09 or
jdk1.5.0_10 on winXP using eclipse debugger, in Netbeans 5.0 and using
javac/java command line.

I have this line in my code;
assert !Double.isNaN(tRating) : "!Double.isNaN(tRating), tRating="+
tRating;

and it is triggering the following AssertionError.

Exception in thread "main" java.lang.AssertionError:
!Double.isNaN(tRating), tRating=3.6119877801230094
    at packages.Netflix.predictRating(Netflix.java:250)
    at packages.Netflix.train(Netflix.java:170)
    at packages.Netflix.main(Netflix.java:122)

At the point the Error is triggered in eclipse, I can inspect the
values, and it is clear that the value is a valid double. However if I
drop to frame and rerun the code, the pointer passes the assertion with
no problem a second time. Also if I rerun the code again, the assertion
is triggered but with a different value of tRating.

Given those symptoms, I would look VERY closely at whatever is supposed
to synchronize accesses and updates to tRating.

It is behaving exactly like a variable that is being updated from at
least one other thread while the assertion executes, so that it is a NaN
when the test is done, but something else when it is converted to String
for concatenation.

Patricia