Java Requires Chilkat v11.1.0+

Regular Expression Replace Capture Groups

See more Regular Expressions Examples

Demonstrates replacing capture groups for a regular expression.

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

Chilkat2 Java

import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.JsonObject;
import com.chilkatsoft.chilkat2.StringBuilder;

public class ChilkatExample {

    public static void main(String[] args) {
        String subject = "John Anders, +_+_+ Mary Robins $$$$";
        String pattern = "(?<first>\\w+)\\s+(?<last>\\w+)";

        StringBuilder sb = new StringBuilder();
        sb.append(subject);

        JsonObject json = new JsonObject();
        json.setEmitCompact(false);

        int timeoutMs = 2000;
        int numMatches = sb.regexMatch(pattern, json, timeoutMs);
        if (numMatches < 0) {
            // Probably an error in the regular expression.
            // Suggestion: Use AI to help create and/or diagnose regular expressions.
            System.out.println(sb.getLastErrorText());
            return;
        }

        // Examine the matches:
        System.out.println(json.emit());

        // There are 2 matches:

        // {
        //   "named": {
        //     "first": 1,
        //     "last": 2
        //   },
        //   "match": [
        //     {
        //       "group": [
        //         {
        //           "cap": "John Anders",
        //           "idx": 0,
        //           "len": 11
        //         },
        //         {
        //           "cap": "John",
        //           "idx": 0,
        //           "len": 4
        //         },
        //         {
        //           "cap": "Anders",
        //           "idx": 5,
        //           "len": 6
        //         }
        //       ]
        //     },
        //     {
        //       "group": [
        //         {
        //           "cap": "Mary Robins",
        //           "idx": 19,
        //           "len": 11
        //         },
        //         {
        //           "cap": "Mary",
        //           "idx": 19,
        //           "len": 4
        //         },
        //         {
        //           "cap": "Robins",
        //           "idx": 24,
        //           "len": 6
        //         }
        //       ]
        //     }
        //   ]
        // }

        // To replace capture groups, write code to examine each capture group within
        // each match, and provide a replacement string.
        // Then call RegexReplace.

        // For example, let's capitalize the first names, and add append "on" to the last name.
        // After doing replacements, we should get:  JOHN Anderson, +_+_+ MARY Robinson $$$$

        int firstNameIdx = json.intOf("named.first");
        int lastNameIdx = json.intOf("named.last");

        StringBuilder sbTemp = new StringBuilder();

        int i = 0;
        numMatches = json.sizeOfArray("match");
        while (i < numMatches) {
            json.setI(i);

            // The replacement string for the first name will be all uppercase.
            json.setJ(firstNameIdx);
            sbTemp.clear();
            json.stringOfSb("match[i].group[j].cap", sbTemp);
            sbTemp.toUppercase();
            json.updateSb("match[i].group[j].rep", sbTemp);

            // Append "on" to the last name.
            json.setJ(lastNameIdx);
            sbTemp.clear();
            json.stringOfSb("match[i].group[j].cap", sbTemp);
            sbTemp.append("on");
            json.updateSb("match[i].group[j].rep", sbTemp);

            i = i + 1;
        }

        // The JSON now has replacement strings:
        System.out.println(json.emit());

        // {
        //   "named": {
        //     "first": 1,
        //     "last": 2
        //   },
        //   "match": [
        //     {
        //       "group": [
        //         {
        //           "cap": "John Anders",
        //           "idx": 0,
        //           "len": 11
        //         },
        //         {
        //           "cap": "John",
        //           "idx": 0,
        //           "len": 4,
        //           "rep": "JOHN"
        //         },
        //         {
        //           "cap": "Anders",
        //           "idx": 5,
        //           "len": 6,
        //           "rep": "Anderson"
        //         }
        //       ]
        //     },
        //     {
        //       "group": [
        //         {
        //           "cap": "Mary Robins",
        //           "idx": 19,
        //           "len": 11
        //         },
        //         {
        //           "cap": "Mary",
        //           "idx": 19,
        //           "len": 4,
        //           "rep": "MARY"
        //         },
        //         {
        //           "cap": "Robins",
        //           "idx": 24,
        //           "len": 6,
        //           "rep": "Robinson"
        //         }
        //       ]
        //     }
        //   ]
        // }

        // Call RegexReplace to update the StringBuilder with the replacements.
        try {
            sb.regexReplace(json);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println("Result after doing replacements:");
        System.out.println(sb.getAsString());

        // Result after doing replacements:
        // JOHN Anderson, +_+_+ MARY Robinson $$$$
    }
}