Matcher replaceFirst(String) method in Java with Examples

The replaceFirst(String) method of Matcher Class behaves as a append-and-replace method. This method reads the input string and replace it with the first matched pattern in the matcher string.

Syntax:

public String replaceFirst(String stringToBeReplaced)

Parameters: This method takes a parameter stringToBeReplaced which is the String to be replaced in the matcher.



Return Value: This method returns a String with the target String contructed by replacing the String.

Below examples illustrate the Matcher.replaceFirst() method:

Example 1:

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// 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 = "GFG";
        StringBuilder builder = new StringBuilder();
  
        // Replace every matched pattern
        // with the target String
        // using replaceFirst() method
        System.out.println("After Replacement: "
                           + matcher
                                 .replaceFirst(stringToBeReplaced));
    }
}

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Output:

Before Replacement: GeeksForGeeks Geeks for For Geeks Geek
After Replacement: GFGForGeeks Geeks for For Geeks Geek

Example 2:

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// 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
            = "FGF FGF FGF 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(stringToBeReplaced));
    }
}

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Output:

Before Replacement: FGF FGF FGF FGF
After Replacement: GFG FGF FGF FGF

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/regex/Matcher.html#replaceFirst-java.lang.String-



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