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The appendReplacement(StringBuffer, String) method of Matcher Class behaves as a append-and-replace method. This method reads the input string and replace it with the matched pattern in the matcher string. Syntax:

public Matcher 
    appendReplacement(StringBuffer buffer, 
                      String stringToBeReplaced)

Parameters: This method takes two parameters:

buffer: which is the StringBuffer that stores the target string.
stringToBeReplaced: which is the String to be replaced in the matcher.

Return Value: This method returns a Matcher with the target String replaced. Exception: This method throws following exceptions:

IllegalStateException: If no match has yet been attempted, or if the previous match operation failed
IllegalArgumentException: If the replacement string refers to a named-capturing group that does not exist in the pattern
IndexOutOfBoundsException: If the replacement string refers to a capturing group that does not exist in the pattern

Below examples illustrate the Matcher.appendReplacement() method: Example 1:

Java

// Java code to illustrate appendReplacement() method

import java.util.regex.*;

public class GFG {
    public static void main(String[] args)
    {

        // Get the regex to be checked
        String regex = "(Geeks)";

        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);

        // Get the String to be matched
        String stringToBeMatched
            = "GeeksForGeeks Geeks for For Geeks Geek";

        // Create a matcher for the input String
        Matcher matcher
            = pattern.matcher(stringToBeMatched);

        System.out.println("Before Replacement: "
                           + stringToBeMatched);

        // Get the String to be replaced
        String stringToBeReplaced = "GEEKS";
        StringBuffer buffer = new StringBuffer();

        // Replace every matched pattern
        // with the target String
        // using appendReplacement() method
        while (matcher.find()) {
            matcher.appendReplacement(buffer,
                                      stringToBeReplaced);
        }
        matcher.appendTail(buffer);

        // Print the replaced matcher
        System.out.println("After Replacement: "
                           + buffer.toString());
    }
}

Output:

Before Replacement: GeeksForGeeks Geeks for For Geeks Geek
After Replacement: GEEKSForGEEKS GEEKS for For GEEKS Geek

Example 2:

Java

// Java code to illustrate appendReplacement() method

import java.util.regex.*;

public class GFG {
    public static void main(String[] args)
    {

        // Get the regex to be checked
        String regex = "(FGF)";

        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);

        // Get the String to be matched
        String stringToBeMatched
            = "FGF FGF FGF FGF";

        // Create a matcher for the input String
        Matcher matcher
            = pattern.matcher(stringToBeMatched);

        System.out.println("Before Replacement: "
                           + stringToBeMatched);

        // Get the String to be replaced
        String stringToBeReplaced = "GFG";
        StringBuffer buffer = new StringBuffer();

        // Replace every matched pattern
        // with the target String
        // using appendReplacement() method
        while (matcher.find()) {
            matcher.appendReplacement(buffer,
                                      stringToBeReplaced);
        }
        matcher.appendTail(buffer);

        // Print the replaced matcher
        System.out.println("After Replacement: "
                           + buffer.toString());
    }
}

Output:

Before Replacement: FGF FGF FGF FGF
After Replacement: GFG GFG GFG GFG

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/regex/Matcher.html#appendReplacement-java.lang.StringBuffer-java.lang.String-

Matcher appendReplacement(StringBuffer, String) method in Java with Examples

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