Matcher replaceAll(Function) method in Java with Examples

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() methodimport 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() methodimport 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
				
					


