Matcher replaceAll(Function) method in Java with Examples - GeeksforGeeks

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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Java - util package
Java-Functions
Java-Matcher
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