Can I replace groups in Java regex

Question

I have this code  and I want to know  if I can replace only groups  not all pattern  in Java regex  Code           Pattern p   Pattern compile     d      d         String input    6 example input 4       Matcher m   p matcher input       if  m find                 Now I want replace group one      d    with number           and group two  too    d    with 1  but I don t know how

User · Accepted Answer

Use  n  where n is a digit  to refer to captured subsequences in replaceFirst       I m assuming you wanted to replace the first group with the literal string  number  and the second group with the value of the first group   Pattern p   Pattern compile     d        d     String input    6 example input 4   Matcher m   p matcher input   if  m find             replace first number with  number  and second number with the first     String output   m replaceFirst  number  3 1        number 46     Consider   D   for the second group instead of          is a greedy matcher  and will at first consume the last digit  The matcher will then have to backtrack when it realizes the final   d  has nothing to match  before it can match to the final digit

User · Answer

Add a third group by adding parens around     then replace the subsequence with  number    m group 2     1   e g    String output   m replaceFirst  number    m group 2     1

User · Answer

Sorry to beat a dead horse  but it is kind-of weird that no-one pointed this out -  Yes you can  but this is the opposite of how you use capturing groups in real life    If you use Regex the way it is meant to be used  the solution is as simple as this    6 example input 4  replaceAll       d          d     number 11      Or as rightfully pointed out by shmosel below    6 example input 4  replaceAll   d     d    number 11         since in your regex there is no good reason to group the decimals at all    You don t usually use capturing groups on the parts of the string you want to discard  you use them on the part of the string you want to keep   If you really want groups that you want to replace  what you probably want instead is a templating engine  e g  moustache  ejs  StringTemplate           As an aside for the curious  even non-capturing groups in regexes are just there for the case that the regex engine needs them to recognize and skip variable text  For example  in     abc   capture me    bcd     you need them if your input can look either like  abcabccapture mebcdbcd  or  abccapture mebcd  or even just  capture me    Or to put it the other way around  if the text is always the same  and you don t capture it  there is no reason to use groups at all

User · Answer

You can use matcher start   and matcher end   methods to get the group positions  So using this positions you can easily replace any text

User · Answer

Here is a different solution  that also allows the replacement of a single group in multiple matches  It uses stacks to reverse the execution order  so the string operation can be safely executed   private static void demo           final String sourceString    hello world         final String regex     hello   world           final Pattern pattern   Pattern compile regex        String result   replaceTextOfMatchGroup sourceString  pattern  2  world - gt  world toUpperCase         System out println result       output  hello WORLD     public static String replaceTextOfMatchGroup String sourceString  Pattern pattern  int groupToReplace  Function lt String String gt  replaceStrategy        Stack lt Integer gt  startPositions   new Stack lt  gt         Stack lt Integer gt  endPositions   new Stack lt  gt         Matcher matcher   pattern matcher sourceString        while  matcher find              startPositions push matcher start groupToReplace            endPositions push matcher end groupToReplace              StringBuilder sb   new StringBuilder sourceString       while    startPositions isEmpty              int start   startPositions pop            int end   endPositions pop            if  start  gt   0  amp  amp  end  gt   0                sb replace start  end  replaceStrategy apply sourceString substring start  end                         return sb toString

User · Answer

You could use Matcher start group  and Matcher end group  to build a generic replacement method   public static String replaceGroup String regex  String source  int groupToReplace  String replacement        return replaceGroup regex  source  groupToReplace  1  replacement      public static String replaceGroup String regex  String source  int groupToReplace  int groupOccurrence  String replacement        Matcher m   Pattern compile regex  matcher source       for  int i   0  i  lt  groupOccurrence  i            if   m find    return source     pattern not met  may also throw an exception here     return new StringBuilder source  replace m start groupToReplace   m end groupToReplace   replacement  toString       public static void main String   args           replace with     what was matched by group 1         input  aaa123ccc        output   123ccc     System out println replaceGroup    a-z     0-9     a-z       aaa123ccc   1                 replace with       what was matched the 4th time by the group 2        input  a1b2c3d4e5        output  a1b2c3d   e5     System out println replaceGroup    a-z     d     a1b2c3d4e5   2  4               Check online demo here

User · Answer

replace the password fields from the input      csrf    9d90c85f-ac73-4b15-ad08-ebaa3fa4a005    originPassword    uaas    newPassword    uaas    confirmPassword    uaas         private static final Pattern PATTERN   Pattern compile     password                                Pattern CASE INSENSITIVE      private static String replacePassword String input  String replacement        Matcher m   PATTERN matcher input       StringBuffer sb   new StringBuffer        while  m find            Matcher m2   PATTERN matcher m group 0          if  m2 find              StringBuilder stringBuilder   new StringBuilder m2 group 0            String result   stringBuilder replace m2 start 1   m2 end 1   replacement  toString            m appendReplacement sb  result                     m appendTail sb       return sb toString            Test   public void test1         String input        csrf      9d90c85f-ac73-4b15-ad08-ebaa3fa4a005      originPassword      123      newPassword      456      confirmPassword      456           String expected        csrf      9d90c85f-ac73-4b15-ad08-ebaa3fa4a005      originPassword              newPassword              confirmPassword                   Assert assertEquals expected  replacePassword input

[java] Can I replace groups in Java regex?

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