Método Matcher replaceFirst(String) en Java con ejemplos

El método replaceFirst() de Matcher Class se comporta como un método de agregar y reemplazar. Este método lee la string de entrada y la reemplaza con el primer patrón coincidente en la string del comparador. 

Sintaxis: 

public String replaceFirst(String stringToBeReplaced)

Parámetros: la string que se reemplazará que es la string que se reemplazará en el comparador.

Tipo de retorno: una string con la string de destino construida reemplazando la string.

Ejemplo 1:

// Java Program to Illustrate replaceFirst() Method
// of Matcher class
 
// Importing required classes
import java.util.regex.*;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Getting the regex to be checked
        String regex = "(Geeks)";
 
        // Creating a pattern from regex
        Pattern pattern = Pattern.compile(regex);
 
        // Getting the String to be matched
        String stringToBeMatched
            = "GeeksForGeeks Geeks for For Geeks Geek";
 
        // Creating a matcher for the input String
        Matcher matcher
            = pattern.matcher(stringToBeMatched);
 
        // Displaying the string to be matched
        // before replacing
        System.out.println("Before Replacement: "
                           + stringToBeMatched);
 
        // Getting the string to be replaced
        String stringToBeReplaced = "GFG";
        StringBuilder builder = new StringBuilder();
 
        // Replacing every matched pattern with the target
        // string using replaceFirst() method
        System.out.println(
            "After Replacement: "
            + matcher.replaceFirst(stringToBeReplaced));
    }
}

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

Ejemplo 2:

// Java Program to Illustrate replaceFirst() Method
 
// Importing required classes
import java.util.regex.*;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Getting the regex to be checked
        String regex = "(FGF)";
 
        // Creating a pattern from regex
        Pattern pattern = Pattern.compile(regex);
 
        // Getting the string to be matched
        String stringToBeMatched = "FGF FGF FGF FGF";
 
        // Creating a matcher for the input String
        Matcher matcher
            = pattern.matcher(stringToBeMatched);
 
        // Printing string on console
        // before replacement
        System.out.println("Before Replacement: "
                           + stringToBeMatched);
 
        // Getting the string to be replaced
        String stringToBeReplaced = "GFG";
        StringBuilder builder = new StringBuilder();
 
        // Replacing every matched pattern with target
        // string using replaceFirst() method and printing
        // the string to be replaced
        System.out.println(
            "After Replacement: "
            + matcher.replaceFirst(stringToBeReplaced));
    }
}

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