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Matcher replaceAll(Function) method in Java with Examples

  • Last Updated : 07 Sep, 2021

The replaceAll(Function) method of Matcher Class behaves as a append-and-replace method. This method replaces all instances of the pattern matched in the matcher with the function passed in the parameter.
Syntax: 
 

public String replaceAll(
        Function replacerFunction)

Parameters: This method takes a parameter replacerFunction which is the function that defines the replacement of the matcher.
Return Value: This method returns a String with the target String constructed by replacing the String.
Exceptions: This method throws following exceptions: 
 

  • NullPointerException: if the replacer function is null
  • ConcurrentModificationException: if it is detected that the replacer function modified this matcher’s state

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

Java




// Java code to illustrate replaceAll() 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";
        StringBuilder builder
            = new StringBuilder();
 
        // Replace every matched pattern
        // with the target String
        // using replaceAll() method
        System.out.println("After Replacement: "
                           + matcher
                                 .replaceAll(
                                     x -> x.group().toUpperCase()));
    }
}

Output: 
 



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

Example 2:
 

Java




// Java code to illustrate replaceAll() 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
            = "GFGFGFGFGFGFGFGFGFG FGF GFG GFG 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)";
        StringBuilder builder
            = new StringBuilder();
 
        // Replace every matched pattern
        // with the target String
        // using replaceAll() method
        System.out.println("After Replacement: "
                           + matcher
                                 .replaceAll(
                                     x -> x.group().toLowerCase()));
    }
}

Output: 
 

Before Replacement: GFGFGFGFGFGFGFGFGFG FGF GFG GFG FGF
After Replacement: GfgfGfgfGfgfGfgfGFG fgf GFG GFG fgf

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/regex/Matcher.html#replaceAll-java.util.function.Function-
 

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