Looking for good table with all Java operators
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From: Lew on 25 Jan 2010 17:13 Robbo wrote: > It means there is mistake in Mr. Doedy Green's table > (http://mindprod.com/jgloss/precedence.html). > In this table prefix and postfix has the same priority -- probably > simple mistake with numbers of precedence. > But more serious mistake in his table is that prefix is before > postfix. According to > <http://java.sun.com/docs/books/tutorial/java/nutsandbolts/operators.html> > postfix goes first. > Roedy has prefix/unary at the same level of precedence as postfix, not at a higher level. Still a difference, but one that makes no difference since right-associativity would still have postfix operators evaluated first. > I really wish official table of Java operators with precedence > and associations. You just cited an official table. Didn't that grant your wish? <<http://java.sun.com/docs/books/tutorial/java/nutsandbolts/ operators.html> (copied and pasted from your post) Why are you asking for something you already have? > In C++ situations is not better. E.g. [sic] here > <http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B> > there is information that postfix has precedence 2 and prefix has > precedence 3. In my Polish edition of Stroustrup's book > postfix and prefix has the same precedence. > That's off topic, but let me suggest that those differences may be due to changes in the language, perhaps. Not that I really know. -- Lew
From: Robbo on 25 Jan 2010 17:20 After reading a few resources, I created such table: Level Category Operator Associativity --------------------------------------------------------------- 1 postfix expr++ expr-- left --------------------------------------------------------------- 2 prefix ++expr --expr right unary +expr -expr right logical NOT ! right bitwise NOT ~ left --------------------------------------------------------------- 3 cast (type) right --------------------------------------------------------------- 4 multiplicative * / % left --------------------------------------------------------------- 5 additive + - left --------------------------------------------------------------- 6 shift << >> >>> left --------------------------------------------------------------- 7 relational < <= > >= left type comparison instanceof --------------------------------------------------------------- 8 equality == != left --------------------------------------------------------------- 9 bitwise AND & left --------------------------------------------------------------- 10 bitwise XOR ^ left --------------------------------------------------------------- 11 bitwise OR | left --------------------------------------------------------------- 12 logical AND && left --------------------------------------------------------------- 13 logical OR || left --------------------------------------------------------------- 14 conditional ?: right --------------------------------------------------------------- 15 assignment = += -= *= /= right %= &= ^= |= <<= >>= >>>= --------------------------------------------------------------- What do you think about this? It contains only real Java operators, I hope. I have a few problems with this table: 1. According to some resources, postfix and prefix have the same level (precedence). It is right? 2. How about associativity of ~ ? 3. How about level (precedence) of "cast"? Shouldn't it be in level 2?
From: Mike Schilling on 25 Jan 2010 17:20 Lew wrote: > Mike Schilling wrote: >> Other way around. Postfix ++ has a higher precedence than the cast >> does. > > I believe the issue here is one of associativity, not precedence. No, it really is precedence. You can't sensibly define associatively among a group of unary operators that include both left-hand and right-hand operators. That's why the two postfix operators (++ and --) are at a precedence level all their own, while the corresponding prefix operators share a level with casts. > Both cast and postfix operators are right-associative, therefore the > postfix operator is evaluated first. Postfix operators aren't associative at all, since you can't use two of them, e.g.. i++++ is iilegal.
From: znôrt on 25 Jan 2010 17:27 On Mon, 25 Jan 2010 23:20:23 +0100, Robbo <nie.mam(a)yle.com> wrote: > What do you think about this? that you ... a). are working on yet another compiler/parser/whatever or b). have way too much time and too little to do :-) bytheway, parenthesis do a great job making abritrarily complex expressions evident to anyone reading any code. they have the (great) added benefit of being language independent and widely recognised. just use them! (if you really are in need for such complex expressions).
From: Mike Schilling on 25 Jan 2010 17:29
Lew wrote: > However, the JLS does refer to 'instanceof' as an > operator. But it's not in the list of operators, so the JLS contradicts itself. It really is the Java programmer's Bible! More seriously, the official JLS definition of "operator" describes only operators made up of special characters; that is, it distinguishes "operator" from "keyword". If "new" were spelled "^" as in InputStream strm = ^FileInputStream(filename); the JLS would presumably call it an operator. If you think of operator as a semantic term rather than a syntactical one, you're likely to define it to include "instanceof" and "new". |