JAVA EE: How to use appendReplacement and appendTail methods of matcher class

Monday 25 December 2017

How to use appendReplacement and appendTail methods of matcher class | Regex in java

Click here to watch on Youtube :
https://www.youtube.com/watch?v=S3dusBPXN7E&list=UUhwKlOVR041tngjerWxVccw

RegexDemo.java

import java.util.regex.Matcher;

import java.util.regex.Pattern;

/**
 * 
 * appendReplacement() and appendTail():
 * 
 * The Matcher appendReplacement() and appendTail() methods are used
 * to replace string tokens in an input text, and append the resulting
 * string to a StringBuffer.
 * 
 * When you have found a match using the find() method, you can call
 * the appendReplacement(). Doing so results in the characters from
 * the input text being appended to the StringBuffer, and the matched
 * text being replaced. Only the characters starting from then end of
 * the last match, and until just before the matched characters are
 * copied.
 * 
 * The appendReplacement() method keeps track of what has been copied
 * into the StringBuffer, so you can continue searching for matches
 * using find() until no more matches are found in the input text.
 * 
 * Once the last match has been found, a part of the input text will
 * still not have been copied into the StringBuffer. This is the
 * characters from the end of the last match and until the end of the
 * input text. By calling appendTail() you can append these last
 * characters to the StringBuffer too.
 *
 * 
 */

public class RegexDemo

{

    public static void main(String[] args)

    {

        String text = "John writes about this, and John Doe writes about that,"

                + " and John Wayne writes about everything.";

        String regex = "(John) ";

        Pattern pattern = Pattern.compile(regex);

        Matcher matcher = pattern.matcher(text);

        StringBuffer stringBuffer = new StringBuffer();

        while (matcher.find())

        {

            matcher.appendReplacement(stringBuffer, "Peter ");

            System.out.println(stringBuffer.toString());

        }

        matcher.appendTail(stringBuffer);

        System.out.println(stringBuffer.toString());

    }

}

Output

Peter

Peter writes about this, and Peter

Peter writes about this, and Peter Doe writes about that, and Peter

Peter writes about this, and Peter Doe writes about that, and Peter Wayne writes about everything.