Replace Letter

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        System.out.println("Ange en mening: ");

        String userInput = input.nextLine();

        System.out.println(replaceLetter(userInput));

    }

    public static String replaceLetter(String userInput)
    {
        char[] letters = userInput.toCharArray();

        for (int i = 0; i < letters.length; i++)
        {
            switch (letters[i])
            {
                case 'g':
                    letters[i] = 'f';
                    break;
            }
        }
        return new String(letters);
    }

}