05. Messages

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = Integer.parseInt(scanner.nextLine()),
                sms;
        String message = "";

        for (int i = 0; i < n; i++) {
            sms = Integer.parseInt(scanner.nextLine());

            switch (sms) {
                    case 2:
                        message += "a";
                        break;
                    case 22:
                        message += "b";
                        break;
                    case 222:
                        message += "c";
                        break;
                    case 3:
                        message += "d";
                        break;
                    case 33:
                        message += "e";
                        break;
                    case 333:
                        message += "f";
                        break;
                    case 4:
                        message += "g";
                        break;
                    case 44:
                        message += "h";
                        break;
                    case 444:
                        message += "i";
                        break;
                    case 5:
                        message += "j";
                        break;
                    case 55:
                        message += "k";
                        break;
                    case 555:
                        message += "l";
                        break;
                    case 6:
                        message += "m";
                        break;
                    case 66:
                        message += "n";
                        break;
                    case 666:
                        message += "o";
                        break;
                    case 7:
                        message += "p";
                        break;
                    case 77:
                        message += "q";
                        break;
                    case 777:
                        message += "r";
                        break;
                    case 7777:
                        message += "s";
                        break;
                    case 8:
                        message += "t";
                        break;
                    case 88:
                        message += "u";
                        break;
                    case 888:
                        message += "v";
                        break;
                    case 9:
                        message += "w";
                        break;
                    case 99:
                        message += "x";
                        break;
                    case 999:
                        message += "y";
                        break;
                    case 9999:
                        message += "z";
                        break;
                    case 0:
                        message += " ";
                        break;
                }
        }
        System.out.println(message);
    }
}

Solution with new switch(Java 21):

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = Integer.parseInt(scanner.nextLine()),
                sms;
        String message = "";

        for (int i = 0; i < n; i++) {
            sms = Integer.parseInt(scanner.nextLine());

            switch (sms) {
                case 2 -> message += "a";
                case 22 -> message += "b";
                case 222 -> message += "c";
                case 3 -> message += "d";
                case 33 -> message += "e";
                case 333 -> message += "f";
                case 4 -> message += "g";
                case 44 -> message += "h";
                case 444 -> message += "i";
                case 5 -> message += "j";
                case 55 -> message += "k";
                case 555 -> message += "l";
                case 6 -> message += "m";
                case 66 -> message += "n";
                case 666 -> message += "o";
                case 7 -> message += "p";
                case 77 -> message += "q";
                case 777 -> message += "r";
                case 7777 -> message += "s";
                case 8 -> message += "t";
                case 88 -> message += "u";
                case 888 -> message += "v";
                case 9 -> message += "w";
                case 99 -> message += "x";
                case 999 -> message += "y";
                case 9999 -> message += "z";
                case 0 -> message += " ";
            };
        }
        System.out.println(message);
    }
}

Solution with array:

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = Integer.parseInt(scanner.nextLine()),
                sms;
        String message = "";

        int[] button = { 32, 0, 97, 100, 103, 106, 109, 112, 116, 119 };

        for (int i = 0; i < n; i++) {
            sms = Integer.parseInt(scanner.nextLine());
            message += (char)(button[sms % 10] + Integer.toString(sms).length() - 1);
        }

        System.out.println(message);
    }
}