Java String.replaceFirst() that takes a “starting from” argument

Question

I need to replace a word in a string looking like \"duh duh something else duh\". I only need to replace the second \"duh\", but the first and the last ones need to stay unt

Answer 1

Will something like this work?

  System.out.println(
     "1 duh 2 duh duh 3 duh"
     .replaceFirst("(duh.*?)duh", "$1bleh")
  ); // prints "1 duh 2 bleh duh 3 duh"

If you just want to replace the second occurrence of a pattern in a string, you really don't need this "starting from" index calculation.

As a bonus, if you want to replace every other duh (i.e. second, fourth, sixth, etc), then just invoke replaceAll instead of replaceFirst.

Answer 2

An alternative using Matcher:

 String input = "duh duh something else duh";
 Pattern p = Pattern.compile("duh");
 Matcher m = p.matcher(input);
 int startIndex = 4;

 String output;

 if (m.find(startIndex)) {
     StringBuffer sb = new StringBuffer();
     m.appendReplacement(sb, "dog");
     m.appendTail(sb);
     output = sb.toString();
 } else {
     output = input;
 }

Answer 3

What about something like this:

String replaceFirstFrom(String str, int from, String regex, String replacement)
{
    String prefix = str.substring(0, from);
    String rest = str.substring(from);
    rest = rest.replaceFirst(regex, replacement);
    return prefix+rest;
}

// or
s.substring(0,start) +  s.substring(start).replaceFirst(search, replace);

just 1 line of code ... not a whole method.