content: import edu.duke.*;
  
  public class CaesarCipher {
      public String encrypt(String input, int key) {
          //Make a StringBuilder with message (encrypted)
          StringBuilder encrypted = new StringBuilder(input);
          //Write down the alphabet
          String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
          //Compute the shifted alphabet
          String shiftedAlphabet = alphabet.substring(key)+
          alphabet.substring(0,key);
          //Count from 0 to < length of encrypted, (call it i)
          for(int i = 0; i < encrypted.length(); i++) {
              //Look at the ith character of encrypted (call it currChar)
              char currChar = encrypted.charAt(i);
              //Find the index of currChar in the alphabet (call it idx)
              int idx = alphabet.indexOf(currChar);
              //If currChar is in the alphabet
              if(idx != -1){
                  //Get the idxth character of shiftedAlphabet (newChar)
                  char newChar = shiftedAlphabet.charAt(idx);
                  //Replace the ith character of encrypted with newChar
                  encrypted.setCharAt(i, newChar);
              }
              //Otherwise: do nothing
          }
          //Your answer is the String inside of encrypted
          return encrypted.toString();
      }
      public void testCaesar() {
          int key = 17;
          FileResource fr = new FileResource();
          String message = fr.asString();
          String encrypted = encrypt(message, key);
          System.out.println(encrypted);  
          String decrypted = encrypt(encrypted, 26-key);
          System.out.println(decrypted);
      }
  }
  
  