ExamPrep - String Manipulator

package com.company;


import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String text = "";
        String line = scanner.nextLine();

        while (!line.equals("End")) {
            String[] tokens = line.split(" +");//тук си извеждаме командата
            String command = tokens[0];

            switch (command) {
                case "Add":
                    text += tokens[1];
                    break;
                case "Upgrade":
                    char charToReplace = tokens[1].charAt(0);
                    char replacer = (char) (charToReplace + 1);
                    text = text.replace(charToReplace, replacer);
                    break;
                case "Print":
                    System.out.println(text);
                    break;
                case "Index":
                    if (text.contains(tokens[1])) {
                        char symbol = tokens[1].charAt(0);
                        for (int i = 0; i < text.length(); i++) {
                            if (text.charAt(i) == symbol) {
                                System.out.print(i + " ");
                            }
                        }
                        System.out.println();
                    } else {
                        System.out.println("None");
                    }
                    break;
                case "Remove":
                    text = text.replace(tokens[1], "");
                    break;
            }


            line = scanner.nextLine();
        }
    }
}