Win a copy of TDD for a Shopping Website LiveProject this week in the Testing forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Paul Clapham
  • Ron McLeod
  • Jeanne Boyarsky
  • Tim Cooke
Sheriffs:
  • Liutauras Vilda
  • paul wheaton
  • Henry Wong
Saloon Keepers:
  • Tim Moores
  • Tim Holloway
  • Stephan van Hulst
  • Carey Brown
  • Frits Walraven
Bartenders:
  • Piet Souris
  • Himai Minh

Regexp question K&b

 
Greenhorn
Posts: 24
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
The first question in K&b book from chapter.6

And the command line:
java Regex2 "\d*" ab34ef
What is the result?
A. 234
B. 334
C. 2334
D. 0123456
E. 01234456
F. 12334567
G. Compilation fails.

Answer given in book is E. Conceptually the answer is correct. But, when
I execute this in my machine, I don't get anyof the above answers. I have
this file in my D:\ drive under the folder :\work\java\scjp.

The first argument that is getting passed is not "\d*" in my case. But it
is "\downloads". downloads is one of my folder in D:\ drive. However
I'm in the d:\work\java\scjp directory. there is no folder by name "downloads" in this directory(d:\work\java\scjp).

The OS is windows XP. So, the above command line argument is "\d*" only
and not "\\d*"(i even tried the second parameter, which is interpreted by
java as "\\d*" and not "\d*", so no output in this case also).

My question is how to pass the parameter "\d*" in case of windows command
prompt. And the second question is why \d* expanded by the OS looks for
a directory under the root directory(D:\) and not the current directory(d:\work\java\scjp) from which the java was invoked.

Thanks,
Krishna.
 
Ranch Hand
Posts: 31
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
have u tried to pass the \d argument with no quotes and see, just consider that even the elements in the array passed in the main method are sent in with no quotes and it will give u a guide
 
Krishnamoorthy Sethuraman
Greenhorn
Posts: 24
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
quote is used to pass a argument containing spaces(from or by the shell to java) (as otherwise it will be split into two parts and be treated two different arguments). So, using or not using quote for a argument not containing space is not going to make any difference(tested this infact).
 
mambe nanje
Ranch Hand
Posts: 31
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
in the K and b book the solution to that problem is specified somewhere that at times that will occur so go in to it and read
 
mambe nanje
Ranch Hand
Posts: 31
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
the extract below is from the k and b book


A similar problem can occur when you hand metacharacters to a Java program
via command-line arguments. If we want to pass the \d metacharacter into our Java
program, our JVM does the right thing if we say
% java DoRegex "\d"
But your JVM might not. If you have problems running the following examples, you
might try adding a backslash (i.e. \\d) to your command-line metacharacters. Don't
worry, you won't see any command-line metacharacters on the exam!
 
Krishnamoorthy Sethuraman
Greenhorn
Posts: 24
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Please don't reproduce the content from book. My question is different from
what you have understood. I'll better stop this thread.
 
author
Posts: 9034
21
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hi Guys,

I think the general policy on this forum is that it's okay to display a question from a book or from a simulator, and that it's okay to display a paragraph or two from a similar source. The strong suggestion is that when you do that you should always credit the author of whatever content is being discussed. I think a thread like this one is totally acceptable. In fact, while can't speak for other authors, Kathy and I really like it when examples from our books are discussed here - even if sometimes you guys find an errata

So keep up the good discussions

Bert
 
author
Posts: 288
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
just a work around:

c:\> java Regex2 \"\d*\" ab34ef

The slightly modified code as follows

 
Ranch Hand
Posts: 127
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I am a little confused on why the m.find() function always interrogates one position beyond the length of the string passed in. Is it because of the 0 to many identifier (the asterisk)? When I try it with \d+ instead, it does what I expect (produces 234 ). I would have expected the method to only go for as many positions that are available (i.e. only produce 0123445).
 
Krishnamoorthy Sethuraman
Greenhorn
Posts: 24
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
yes, it was because of the 0 to many modifer. A match on the empty string("") for the pattern \d* will give the first execution of match.find() as 0.
 
Being a smart alec beats the alternative. This tiny ad knows what I'm talking about:
free, earth-friendly heat - a kickstarter for putting coin in your pocket while saving the earth
https://coderanch.com/t/751654/free-earth-friendly-heat-kickstarter
reply
    Bookmark Topic Watch Topic
  • New Topic