Matcher replaceFirst(Function) method in Java with Examples
The replaceFirst(Function) method of Matcher Class behaves as a append-and-replace method. This method replaces first instance of the pattern matched in the matcher with the function passed in the parameter.
Syntax:
public String replaceFirst(
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.replaceFirst() method:
Example 1:
// Java code to illustrate replaceFirst() 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 replaceFirst() method        System.out.println("After Replacement: "                           + matcher                                 .replaceFirst(                                     x -> x.group().toUpperCase()));    }} |
Output:
Before Replacement: GeeksForGeeks Geeks for For Geeks Geek After Replacement: GEEKSForGeeks Geeks for For Geeks Geek
Example 2:
// Java code to illustrate replaceFirst() 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            = "GFG 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 replaceFirst() method        System.out.println("After Replacement: "                           + matcher                                 .replaceFirst(                                     x -> x.group().toLowerCase()));    }} |
Output:
Before Replacement: GFG FGF GFG GFG FGF After Replacement: GFG fgf GFG GFG FGF
