'\u000a' and '\u000d'
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From: dimakura on 20 Feb 2007 04:22 On Feb 19, 7:10 pm, Andreas Leitgeb <a...(a)gamma.logic.tuwien.ac.at> wrote: > Chris Uppal <chris.up...(a)metagnostic.REMOVE-THIS.org> wrote: > > dimakura wrote: > >> but i can not find why i can not use > >> // char c = '\u000a' > >> is it because '\u000a' is equivivalent to \n and this type is comment > >> is a single-line? > > Yes, exactly right. > > And to test yourself, whether you've really understood, > predict what the compiler will say to that: > > // char c = '\u000a//' > > // :-) yes, i understand: new line begin with comment! ok. just to test myself: it is not an error: // \u000a but error is // \u000a something_else where "something_else" is not spaces or something placed in correct Java-style comment
From: Patricia Shanahan on 20 Feb 2007 04:39 dimakura wrote: > On Feb 19, 7:10 pm, Andreas Leitgeb <a...(a)gamma.logic.tuwien.ac.at> > wrote: >> Chris Uppal <chris.up...(a)metagnostic.REMOVE-THIS.org> wrote: >>> dimakura wrote: >>>> but i can not find why i can not use >>>> // char c = '\u000a' >>>> is it because '\u000a' is equivivalent to \n and this type is comment >>>> is a single-line? >>> Yes, exactly right. >> And to test yourself, whether you've really understood, >> predict what the compiler will say to that: >> >> // char c = '\u000a//' >> >> // :-) > > > yes, i understand: new line begin with comment! > ok. > > just to test myself: > > it is not an error: > > // \u000a > > but error is > > // \u000a something_else > > where "something_else" is not spaces or something placed in correct > Java-style comment > It is not an error. It is two lines of code, and something_else is on the second line, not part of the one line comment. In the following valid program, ("Hello, world"); is neither spaces nor a Java-style comment. public class HelloWorld{ public static void main(String[] args){ System.out.println // \u000a ("Hello, world"); } } Patricia
From: Gordon Beaton on 20 Feb 2007 04:44 On 20 Feb 2007 01:22:55 -0800, dimakura wrote: > but error is > > // \u000a something_else > > where "something_else" is not spaces or something placed in correct > Java-style comment Not just comments and whitespace. It's valid if something_else is anything that can appear at the start of a line, including statements or declarations, etc, in the context of the most recent non-comment before this line, e.g.: public class // \u000a Foo { } /gordon -- [ don't email me support questions or followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e
From: Knute Johnson on 20 Feb 2007 18:02 Gordon Beaton wrote: > > Read section 3.2 of the JLS, which describes translation of the input > to the compiler. The unicode escape sequences are translated into > their corresponding unicode characters, *then* the resulting sequence > of characters is tokenized. > > So when you escape a line feed as you've done, you are essentially > writing this (illegal) code: > > > char c = ' > ' > > i.e. the closing quote ends up on the following line. > > Similarly, commenting the line results in this invalid sequence: > > // char c = ' > ' > > /gordon > Gordon: char c = \u0027\u002a\u0027\u003b Do you know why they would process the unicode prior to determining if it was part of a comment or literal first? It does provide for some great obfuscation. I'm really glad it wasn't me that ran across this, I could have spent days trying to figure this one out :-). -- Knute Johnson email s/nospam/knute/
From: Chris Uppal on 20 Feb 2007 18:55
Knute Johnson wrote: > char c = \u0027\u002a\u0027\u003b > > Do you know why they would process the unicode prior to determining if > it was part of a comment or literal first? I presume the idea is to allow the use of Unicode characters in identifiers and comments without making the source completely inaccessible to people using non-Unicode editors. Also to allow for the case where the source has to be manipulated by non-Unicode programs (source code control, and so on). -- chris |