Hi there,

I have a string which denotes a filename which optionally may have an
extension. Because I need to create an extra (supporting) file which will
contain basic certificates I decided to add (or change if its already there) an
extension .crt to denote the certificates.

After checking up on java.io and java.nio I found nothing to seperate an
extension so I decided to utilize regular expressions since I'm fairly familiar
with them on *nix. However, to my surprise the idea I had isn't working and I
can't think of anything else (not yet anyway) to solve this puzzle...

public void change_name() {

 String filename = "filename.extension";
 String regexp = "\..*$";
 String new_ext = ".crt";

 System.out.println( filename.replaceAll(regexp, new_ext));
}

When trying to compile this it will give you an error saying that the regexp.
is using an "illegal escape character". I can find a mention of this in the
documentation, the page about regexps. states (I quote:) "It is an error to use
a backslash prior to any alphabetic character that does not denote an escaped
construct; these are reserved for future extensions to the regular-expression
language.".

Well, this *does* denote an escape construct since I'm trying to grab a literal
. after which the rest of the string follows untill the end of the line. Trying
to use other constructions like \Q and \E (literal / end literal) but those
give me an error as well.

I've managed to come up with an alternative but it isn't pretty :-(. Could
someone please point me to a more suitable solution or perhaps indicate
something obvious which I missed ?

Solution so far:

public void change_name() {

 //String regexp = "\..*$";
 int index = 0;
 String filename = "filename.extension";
 String new_ext = "crt";
 StringBuffer new_name = new StringBuffer();

 // Determine where the . is located
 for (int i = filename.length() - 1; i > 0; i--) {
   file (filename.charAt(i) == '.') { index = i; break; }
 }
 
 // Construct the filename without extension
 for (int i = 0; i < (filename.length() - index - 1); i++) {
   new_name.append(filename.charAt(i));
 }
 
 // Add the new extension
 new_name.append(new_extension);

 System.out.println("Old filename: " + filename);
 System.out.println("New filename: " + new_name);
}

Thanks in advance.