Matcher replaceAll(String) method in Java with Examples

The replaceAll(String) method of the Matcher class is used to replace every substring that matches a regular expression with a specified replacement string. It scans the entire input sequence and returns a new string containing all the replacements.

• Uses the regular expression associated with the Matcher object.
• Supports capturing groups ($1, $2, etc.) in the replacement string.
• Commonly used for text formatting, filtering, and data cleaning.

Example: Replacing All Occurrences of a Word

import java.util.regex.*;

public class Geeks {

    public static void main(String[] args) {

        // Input string
        String text = "Java is easy. Java is powerful.";

        // Create pattern and matcher
        Pattern pattern = Pattern.compile("Java");
        Matcher matcher = pattern.matcher(text);

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

        // Replace all occurrences
        String result = matcher.replaceAll("Python");

        System.out.println("After Replacement: " + result);
    }
}

Before Replacement: Java is easy. Java is powerful.
After Replacement: Python is easy. Python is powerful.

Explanation: The regular expression matches every occurrence of "Java" in the input string. The replaceAll() method replaces each match with "Python" and returns the updated string.

Syntax

public String replaceAll(String replacement)

• Parameters: The string that replaces every substring matching the regular expression.
• Return Value: Returns a new String in which all matches are replaced with the specified replacement string.

Example: Replacing All Digits

import java.util.regex.*;

public class Geeks {

    public static void main(String[] args) {

        // Input string
        String text = "Order123 will arrive on 25-07-2026.";

        // Create pattern and matcher
        Pattern pattern = Pattern.compile("\\d");
        Matcher matcher = pattern.matcher(text);

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

        // Replace all digits
        String result = matcher.replaceAll("#");

        System.out.println("After Replacement: " + result);
    }
}

Before Replacement: Order123 will arrive on 25-07-2026.
After Replacement: Order### will arrive on ##-##-####.

Explanation: The regular expression \\d matches every digit in the input string. The replaceAll() method replaces each digit with #, producing a new string while leaving the original string unchanged.

Advantages of replaceAll(String) Method

• Replaces all matching substrings in a single method call.
• Returns a new string without changing the original string.
• Supports powerful regular expressions for complex replacements.
• Useful for text formatting, data masking, and input sanitization.
• Simplifies bulk text replacement operations using the Matcher class.