Re: short circuit operators

From:

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

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 25 Feb 2008 16:17:44 +0000

Message-ID:

<fpupn8$4vu$2@south.jnrs.ja.net>

Thomas.a.mcglynn@nasa.gov wrote:

On Feb 24, 7:28 pm, Joshua Cranmer <Pidgeo...@verizon.invalid> wrote:

Stefanie Ertheld wrote:

Well I guess I know why an "AND" has higher precedence than an "OR" -
because that's the rule logical operators are defined in general (even
though for this I still don't completly know the reason, but maybe there
is none).

Boolean AND is roughly equivalent to algebraic multiplication and
boolean OR is roughly equivalent to algebraic addition (aside:
bitwise-or and bitwise-xor have equal precedence). Multiplication has a
higher precedence than addition, so their boolean correspondents have
the same precedence. I am also guessing that (a AND b) OR (c AND d) is
slightly more prevalent than (a OR b) AND (c OR d), but I don't think
that consideration entered into play when deciding precedence.

To me the analogy with multiplication and addition doesn't seem very
compelling.

I guess you haven't studied boolean algebra then?

However in SQL the logical operator AND has precedence
over OR.

If the only reason was "because SQL does it", then it wouldn't be very
compelling to me either.

So for whatever reason this precedence has rather long
precedent - back to the 70's or so if not further.

A little further back, to Boole himself in the mid C19th.

--
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555