replaceAll and hex characters

[Stuart Rogers]

Greetings all,

I'm trying transmorgify this Perl subroutine which replaces various characters and groups of characters with either nulls or spaces

sub fixWhitespace($)
{
  my ( $strToBeFixed_ref) = @_;  # a REFERENCE to a scalar
  
  print "entering fixWhitespace\n" if $debug;

  # NOTE the DEREFERENCING
  $$strToBeFixed_ref =~ s/[\x00]//g ;   # remove all NULLs
  $$strToBeFixed_ref =~ s/[\x0d\x0a]/\x20/g ;   # CRLF to space
  $$strToBeFixed_ref =~ s/[\x7c]/\x20/g ;   # vertical-bar character '|' to space
  $$strToBeFixed_ref =~ s/<data:.+?>/\x20/g ;   # any datastream to space
  $$strToBeFixed_ref =~ s/[^\x20-\x7e]/\x20/g ;   # anything except printable-lower-ascii to space

  #this always comes last
  $$strToBeFixed_ref =~ s/\s{20}//g ;     # remove whitespace in 20-char chunks

  print "exiting  fixWhitespace\n" if $debug;
  return;
}

and came up with this

    public static void trimStringOfNaughtyCharacters( String strToBeTrimmed)
    {
    	strToBeTrimmed.replaceAll("\\x00", null);           // remove all NULLs
    	strToBeTrimmed.replaceAll("\\x0d|\\x0a","\\x20");   // CRLF to spac
    	strToBeTrimmed.replaceAll("\\x7c","\\x20") ;        // vertical-bar character '|' to space
    	strToBeTrimmed.replaceAll("<data:.+?>","\\x20"); ;  // any datastream to space
    	strToBeTrimmed.replaceAll("^\\x20-\\x7e]","\\x20"); // anything except printable-lower-ascii to space
    	
    	// this always comes last
    	strToBeTrimmed.replaceAll("\\s{20}",null);          // remove whitespace in 20-char chunks
    }

to be called like this

       trimStringOfNaughtyCharacters( String strToBeTrimmed)

which compiles but doesn't seem to replace anything.

Any suggestions/pointers/constructive criticism is appreciated.

TIA,

Still-learning Steve

[Rob Spoor]

Strings are immutable. When you call replaceAll, it does not modify the original String but instead returns the result. You need to use this result:

// return String, not void
    public static String trimStringOfNaughtyCharacters( String strToBeTrimmed)
    {
    	strToBeTrimmed = strToBeTrimmed.replaceAll("\\x00", null);           // remove all NULLs
    	// similar for the others
    	
    	// this always comes last
    	strToBeTrimmed = strToBeTrimmed.replaceAll("\\s{20}",null);          // remove whitespace in 20-char chunks

    	return strToBeTrimmed;
    }

Now, when you call this method, you should assign the result value to your original String reference:

       strToBeTrimmed = trimStringOfNaughtyCharacters(String strToBeTrimmed);

By the way, shouldn't you use "" instead of null for the replacement values? I thought that null would cause a runtime exception.

[Stuart Rogers]

Thanks for replying!

Yes you are correct on both counts. It's working now. Thanks and Happy Holidays!


CASE CLOSED

Still-learning Steve

[Rob Spoor]

You're welcome.

[Richard Tookey]

There are a several issues with your code.

First, in the line

$$strToBeFixed_ref =~ s/[^\x20-\x7e]/\x20/g ;   # anything except printable-lower-ascii to space

the comment does not reflect regular expression. The regex says replace anything outside of space to tilde inclusive with a space.

Second, as far as I can see, the 3 separate replaceAll() statements that replace characters with a space can be merged to just one.

        strToBeTrimmed = strToBeTrimmed.replaceAll("<data:.+?>"
                + "|"
                + "[[^ -~][|]]", " ");

Third, the use of hex values makes your regular expressions just about unreadable.

Fourth, the 'null' replacement values will cause a NPE !