QuizWeek1/LoopFun.java

public class LoopFun
{

      /**
       * Given a number, return the factorial of that number.
       * For example, given 5, the factorial is 5 x 4 x 3 x 2 x 1 which should return 120.
       * @param number
       * @return the factorial of the number
       */
      public int factorial(int number){
          int factorial = 1;
          for(int i = 1; i <= number; i++) {
              factorial *= i;
            }  
          return factorial;
      }

      /**
       * Given a phrase, get the acronym of that phrase. Acronym is the combination of
       * the first character of each word in upper case.
       * For example, given "Ruby on Rails", this method will return "ROR"
       * @param phrase
       * @return Upper case string of the first letter of each word
       */
      public String acronym(String phrase) {
          StringBuilder acronym = new StringBuilder();
          acronym.append(phrase.charAt(0));
          for(int i = 0; i < phrase.length(); i++){
              if(Character.isWhitespace(phrase.charAt(i))) {
                  acronym.append(phrase.charAt(i + 1));
              }
          }
          return acronym.toString().toUpperCase();
      }

      /**
       * To prevent anyone from reading our messages, we can encrypt it so it will only be readable by its
       * intended audience. This method encrypt the message by shifting the letter by 3 characters. If the character is
       * at the end of the alphabet, it will wraps around.
       * For example:
       *  'a' => 'd'
       *  'w' => 'z'
       *  'x' => 'a'
       *  'y' => 'b'
       * @param word
       * @return the encrypted string by shifting each character by three character
       */
      public String encrypt(String word) {
          String alphabet = "abcdefghijklmnopqrstuvwxyz";

          StringBuilder encryptedWord = new StringBuilder();
          for(int i = 0; i < word.length(); i++) {
              char letter = word.charAt(i);
              int index = 0;
              if(alphabet.indexOf(letter + 3) == -1) {
                  index = ((alphabet.indexOf(letter) - 26) + 3);
              } else {
                  index = alphabet.indexOf(letter + 3);
              }
              encryptedWord.append(alphabet.charAt(index));
          }
          return encryptedWord.toString();
      }
}