(Demo) String Manipulator - Softuni ivan

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

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);


        StringBuilder finalString = new StringBuilder();

        String input = scanner.nextLine();

        while (!input.toLowerCase().equals("end")) {
            if (input.toLowerCase().equals("end")) {
                break;

            }
            String[] tokens = input.split(" +");
            if (tokens[0].toLowerCase().equals("add")) {
                finalString.append(tokens[1]);
            } else if (tokens[0].toLowerCase().equals("upgrade")) {
                for (int i = 0; i < finalString.length(); i++) {
                    char currentChar = finalString.charAt(i);
                    int charNumber = currentChar + 1;
                    char replaceWith = (char) charNumber;

                    if (currentChar == tokens[1].charAt(0)) {

                        finalString.setCharAt(i, replaceWith);
                    }

                }


            } else if (tokens[0].toLowerCase().equals("print")) {
                System.out.println(finalString.toString());
            } else if (tokens[0].toLowerCase().equals("index")) {
                int counter = 0;
                for (int i = 0; i < finalString.length(); i++) {
                    char currentChar = finalString.charAt(i);
                    if (currentChar == tokens[1].charAt(0)) {
                        System.out.print(i + " ");
                        counter++;
                    }
                }
                if (counter == 0) {
                    System.out.println("None");
                }
                System.out.println();

            } else if (tokens[0].toLowerCase().equals("remove")) {
                // bbrbcbdbbrb
                // bbrb
//                StringBuilder foundedWords = new StringBuilder();
                String currentStringForRemove = tokens[1];

                delete(finalString, currentStringForRemove);


            } else {
                System.out.println("nevalidna komanda!");

            }
            input = scanner.nextLine();
        }


    }

    public static void delete(StringBuilder sb, String s) {

//        while (sb.toString().contains(s)) {

        for (int c = 0; c < sb.length(); c++) {
            int start = c;
//            if (sb.length() == s.length()) {
//                break;
//            }
            StringBuilder emptySb = new StringBuilder();
            for (int i = start; i < start + s.length(); i++) {
                emptySb.append(sb.toString().charAt(i));
            }
            if (emptySb.toString().equals(s)) {
                sb.delete(start, start + s.length());

            }
        }


//
//        }

    }
}