Sentence Cipher

/in /by

 This assignment will
consist of a single class, with all code in the main() method. Call your
class SentenceCipher (that
is, the source code will be in a file called SentenceCipher.java). If you
choose to use an IDE other than DrJava, ensure that your program is not defined
in a package (there should be no package statement at the top of the file).

When your assignment is complete, a user running your program will
be prompted to enter the shared ‘source’ text, then asked if they want to
encrypt or decrypt a message. The source text may contain any mixture of
characters, including punctuation and spaces. Before continuing, the source
text must be converted to all lower case.

After receiving the source text from the user, they will be asked
to choose one of two options:

  1. Encrypt a
    message
  • The user is
    prompted to enter a word to be encrypted (this word is converted to lower
    case).
  • The program
    finds the position in the source text of the first occurrence of each
    character from the word (or -1 if the character cannot be found) and
    creates a new String containing those positions, separated by spaces and
    ending with -2.
  • The program
    displays the list of positions, preceded by the text “Result: ”.

1. 
On a separate line, the
program outputs the amount of information loss, which is charactersnotfoundwordlength×100

  • This should be
    preceded by “Information loss (%): ”.
  • Decrypt a
    message
    • The user is
      prompted to enter a list of positions, separated by spaces and ending
      with -2 (to indicate the end of the word).
    • As long as the
      next position is not -2, the program reconstructs the word one character
      at a time:
      • if the
        position is within the bounds of the source text then the character at
        that position is added to the word;
      • if the
        position is -1 then an underscore (_) is appended to the string,
        indicating an unrecoverable character; and
      • if the
        position is less than -1 or beyond the end of the source text then an
        exclamation mark (!) is appended to the word.
    • If there were
      any invalid positions (less than -1 or beyond the end of the source text)
      then the program should print a message indicating how many. The number
      should be followed by the text ” invalid position(s)“. The message
      should not be displayed at all if there were no invalid positions.
    • The program
      outputs the recovered message, preceded by the text “Result: ”
    • On a separate
      line, the program outputs the amount of information loss, which is charactersnotfoundwordlength×100, , where the number of
      characters not found includes both positions of -1 and invalid positions.
      This should be preceded by “Information loss (%): ”.