Caesar's Cipher
Overview¶
In a Caesar’s Cipher, you shift each letter of the alphabet a set amount to encode a message. For example with a shift of 3, the message “DOG” becomes “GRJ”, but with a shift of 7 "DOG" becomes "KVN".
You will write a program that will encrypt and decrypt text using Caesar's Cipher.
Structure¶
Starter code: CaesarCipher/src/com.example.caesarcipher/CaesarCipher
Starter code tests: CaesarCipher/test/com.example.caesarcipher/CaesarCipherTests
The CaesarCipher class has two method stubs, one that encrypts a message and another that decrypts the message. Each method accepts a String and a numeric shift amount, and will return the encrypted or decrypted String.
CaesarCipher also has two private method stubs, for encrypting or decrypting a single character. These are to be used by the public encrypt and decrypt methods. You are welcome to factor your code into additional methods if you choose.
Test-Driven Development¶
Almost all JUnit tests in CaesarCipherTests will fail at first. Your task is to add code to the encrypt and decrypt methods, and to encryptChar and decryptChar, to get each test method to pass, one test method at a time.
Verify that all JUnit tests pass before writing a user-facing application that uses the CaesarCipher class.
Hint: Remember characters are simply numbers behind the scenes
Caesar Cipher Application¶
Once you get the JUnit tests to pass, create an application class with a main that prompts the user for the message as well as the shift amount. It should use an instance of CaesarCipher to do the work. Try to organize your application code into methods, rather than one massive main. For example, a method that prompts for and returns the input message, another that prompts for and returns the shift amount.
Prerequisite¶
Implement the methods in the CaesarCipher class so that all JUnit tests in CaesarCipherTests pass.
User Story #1¶
The user is asked if they would like to encrypt or decrypt a message.
User Story #2¶
The user is now prompted to input the message in question.
User Story #3¶
The user is now asked by what shift amount they would like to encrypt or decrypt the message.
User Story #4¶
The message is then displayed in its encrypted or decrypted state depending on the selection in step 1.
- Can you decipher the message "Or fher gb qevax lbhe binygvar" with a shift of 13?