Still, should not findInLine() in principle work in the way I
expected it to? Unless I made some blatant mistake there, I'll file
a bug.
I did (make a mistake, that is).
Read the source for Scanner.
Is this available? I did a quick search, but could not find it either
locally nor on the web.
findInLine() eventually calls findWithinHorizon().
findWithinHorizon() is documented as using non-anchoring bounds.
"The scanner treats the horizon as a transparent, non-anchoring
bound (see {@link Matcher#useTransparentBounds} and {@link
Matcher#useAnchoringBounds})."
The description of Matcher.useAnchoringBounds() makes it clear that
^ and $ meta-chars are only recognized when using anchoring bounds.
Therefore, findWithinHorizon() appears to not recognize ^ and $, and
it does so intentionally (i.e. the behavior is documented).
Oh, I had not seen that previously.
Personally, I wouldn't use a Pattern to match a single literal like
"ATOM". I'd just use readLine() on the Reader and
string.startsWith(). Or readLine() and then apply an anchored
Matcher to the line if the possible starting patterns were more than
a single literal. Scanner appears to intentionally set the pattern
to non-anchoring (search its source for useAnchoring), which doesn't
seem very line-oriented to me.
After reading some more, it turns out there is another part of the
docs which I had missed: because Scanner uses non-anchoring bounds,
these are not matched by ^ and $, but line ends should be nonetheless.
However: "In multiline mode the expressions ^ and $ match just after
or just before, respectively, a line terminator or the end of the
input sequence. By default these expressions only match at the
beginning and the end of the entire input sequence. "
So, I get the desired behaviour after switching to this Pattern:
Pattern atomP = Pattern.compile("^ATOM", Pattern.MULTILINE);
Thank you very much to everyone who responded!
A.
--
Ansgar Esztermann
DV-Systemadministration
Max-Planck-Institut für biophysikalische Chemie, Abteilung 105
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