Java Regex Replace with Capturing Group

Question

Is there any way to replace a regexp with modified content of capture group   Example   Pattern regex   Pattern compile     d 1 2      Matcher regexMatcher   regex matcher text   resultString   regexMatcher replaceAll   1        3      And I d like to replace all occurrence with  1 multiplied by 3   edit   Looks like  something s wrong     If I use  Pattern regex   Pattern compile     d 1 2      Matcher regexMatcher   regex matcher  12 54 1 65    try       String resultString   regexMatcher replaceAll regexMatcher group 1      catch  Exception e        e printStackTrace        It throws an IllegalStateException  No match found  But  Pattern regex   Pattern compile     d 1 2      Matcher regexMatcher   regex matcher  12 54 1 65    try       String resultString   regexMatcher replaceAll   1      catch  Exception e        e printStackTrace        works fine  but I can t change the  1     edit   Now  it s working

User · Answer

Java 9 offers a Matcher replaceAll   that accepts a replacement function   resultString   regexMatcher replaceAll          m - gt  String valueOf Integer parseInt m group      3

User · Answer

Source  java-implementation-of-rubys-gsub  Usage        Rewrite an ancient unit of length in SI units  String result   new Rewriter    0-9       0-9      -    inch es            public String replacement             float inches   Float parseFloat group 1            return Float toString 2 54f   inches      cm           rewrite  a 17 inch display    System out println result       The  Searching and Replacing with Non-Constant Values Using a    Regular Expression  example from the Java Almanac  result   new Rewriter    a-zA-Z   0-9            public String replacement             return group 1  toUpperCase            rewrite  ab12 cd efg34    System out println result     Implementation  redesigned      import static java lang String format   import java util regex Matcher  import java util regex Pattern   public abstract class Rewriter       private Pattern pattern      private Matcher matcher       public Rewriter String regularExpression            this pattern   Pattern compile regularExpression              public String group int i            return matcher group i              public abstract String replacement   throws Exception       public String rewrite CharSequence original            return rewrite original  new StringBuffer original length     toString               public StringBuffer rewrite CharSequence original  StringBuffer destination            try               this matcher   pattern matcher original               while  matcher find                      matcher appendReplacement destination                       destination append replacement                               matcher appendTail destination               return destination            catch  Exception e                throw new RuntimeException  Cannot rewrite     toString    e                         Override     public String toString             StringBuilder sb   new StringBuilder            sb append pattern pattern             for  int i   0  i  lt   matcher groupCount    i                sb append format   n t  s  -  s   i  group i             return sb toString

User · Answer

How about       if  regexMatcher find          resultString   regexMatcher replaceAll              String valueOf 3   Integer parseInt regexMatcher group 1          To get the first match  use  find    After that  you can use  group 1  to refer to this first match  and replace all matches by the first maches value multiplied by 3   And in case you want to replace each match with that match s value multiplied by 3       Pattern p   Pattern compile     d 1 2          Matcher m   p matcher  12 54 1 65        StringBuffer s   new StringBuffer        while  m find            m appendReplacement s  String valueOf 3   Integer parseInt m group 1          System out println s toString       You may want to look through Matcher s documentation  where this and a lot more stuff is covered in detail

User · Answer

earl s answer gives you the solution  but I thought I d add what the problem is that s causing your IllegalStateException  You re calling group 1  without having first called a matching operation  such as find     This isn t needed if you re just using  1 since the replaceAll   is the matching operation

[java] Java Regex Replace with Capturing Group

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