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Matcher replaceFirst() method in Java with Examples
The java.util.regex.Matcher class represents an engine that performs various match operations. There is no constructor for this class, you can create/obtain an object of this class using the matches() method of the class java.util.regex.Pattern.
The replaceFirst() method of this (Matcher) class accepts a string value and, replaces the first matched subsequence in the input text with the given string value and returns the result.
Example 1
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class ReplaceFirstExample {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter input text: ");
String input = sc.nextLine();
String regex = "[#]";
//Creating a pattern object
Pattern pattern = Pattern.compile(regex);
//Creating a Matcher object
Matcher matcher = pattern.matcher(input);
int count =0;
while(matcher.find()) {
count++;
}
//Retrieving Pattern used
System.out.println("The are character # occurred "+count+" times in the given text");
//Replacing the first occurrence with @
String result = matcher.replaceFirst("@");
System.out.println("Text after replacing the first occurrence of # with @ \n"+result);
}
}Output
Enter input text: Enter input text: Hello# How # are# you #welcome to Tutorials#point The are character # occurred 5 times in the given text Text after replacing the first occurrence of # with @ Hello@ How # are# you #welcome to Tutorials#point
Example 2
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class ReplaceFirstExample {
public static void main(String args[]) {
//Reading String from user
System.out.println("Enter a String");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String regex = "\s+";
//Compiling the regular expression
Pattern pattern = Pattern.compile(regex);
//Retrieving the matcher object
Matcher matcher = pattern.matcher(input);
//Replacing all space characters with single space
String result = matcher.replaceFirst("_");
System.out.print("Text after replacing the first space with '_': \n"+result);
}
}Output
Enter a String hello this is a sample text with irregular spaces Text after replacing the first space with '_': hello_this is a sample text with irregular spaces
Updated on: 20-Nov-2019
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