replaceFirst String Method not working

Question

Below is the code :

String title = '(AB - QWER) Manager';
String titlePrefix = '(CD - DASF)';
String regex = '^(\\([A-Z][A-Z] - [A-Z][A-Z][A-Z][A-Z]\\))$';
if(title != null && !title.startsWith(titlePrefix)) {
    //Get the prefix from the title
    String[] parts;
    String prefix = '';
    parts = title.split('\\)',2);
    if(parts.size() > 0 ) {
        prefix = parts[0] + ')';
    }
    
    Pattern TitlePattern = Pattern.compile(regex);
    Matcher prefixMatcher = TitlePattern.matcher(prefix);
    System.debug('prefixMatcher::'+prefixMatcher.matches());
    if(prefixMatcher.matches()){
        prefix=titlePrefix; 
        title = title.replaceFirst(regex, prefix);
        System.debug('Prefix0::'+prefix);
        System.debug('NewTitle::'+ title);
    }
}

I am trying to update the prefix of the title to the titlePrefix using replaceFirst Function, but it doesn't work. My End Result should be : title = '(CD - DASF) Manager'

Answer 1

Your solution is incredibly over-complicated.

You just need to write:

String title = '(AB - QWER) Manager';
String titlePrefix = '(CD - DASF)';
String regex = '^\\([A-Z]{2} - [A-Z]{4}\\)';
String output = title?.replaceFirst(regex, titlePrefix);
System.debug(output);

Where ?. is the Safe Navigation Operator (so, if null, it just returns null early), and ^\\([A-Z]{2} - [A-Z]{4}\\) matches (XX - XXXX) (where X is any letter), but only if it is at the beginning of the string (^). If the match is not found, the original string is returned.