Java/ciphers/Caesar.java at master · kdzxiaoli/Java · GitHub

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packageciphers;

importjava.util.Scanner;

/**
 *
 * A Java implementation of Caesar Cipher. /It is a type of substitution cipher
 * in which each letter in the plaintext is replaced by a letter some fixed
 * number of positions down the alphabet. /
 *
 * @author FAHRI YARDIMCI
 * @author khalil2535
 */
publicclassCaesar {

/**
 * Encrypt text by shifting every Latin char by add number shift for ASCII
 * Example : A + 1 -> B
 *
 * @param message
 * @param shift
 * @return Encrypted message
 */
publicstaticStringencode(Stringmessage, intshift) {
Stringencoded = "";

while (shift >= 26) { // 26 = number of latin letters
shift -= 26;
 }

finalintlength = message.length();
for (inti = 0; i < length; i++) {

// int current = message.charAt(i); //using char to shift characters because ascii is in-order latin alphabet
charcurrent = message.charAt(i); // Java law : char + int = char

if (IsCapitalLatinLetter(current)) {

current += shift;
encoded += (char) (current > 'Z' ? current - 26 : current); // 26 = number of latin letters

 } elseif (IsSmallLatinLetter(current)) {

current += shift;
encoded += (char) (current > 'z' ? current - 26 : current); // 26 = number of latin letters

 } else {
encoded += current;
 }
 }
returnencoded;
 }

/**
 * Decrypt message by shifting back every Latin char to previous the ASCII
 * Example : B - 1 -> A
 *
 * @param encryptedMessage
 * @param shift
 * @return message
 */
publicstaticStringdecode(StringencryptedMessage, intshift) {
Stringdecoded = "";

while (shift >= 26) { // 26 = number of latin letters
shift -= 26;
 }

finalintlength = encryptedMessage.length();
for (inti = 0; i < length; i++) {
charcurrent = encryptedMessage.charAt(i);
if (IsCapitalLatinLetter(current)) {

current -= shift;
decoded += (char) (current < 'A' ? current + 26 : current);// 26 = number of latin letters

 } elseif (IsSmallLatinLetter(current)) {

current -= shift;
decoded += (char) (current < 'a' ? current + 26 : current);// 26 = number of latin letters

 } else {
decoded += current;
 }
 }
returndecoded;
 }

/**
 *
 * @param c
 * @return true if character is capital Latin letter or false for others
 */
privatestaticbooleanIsCapitalLatinLetter(charc) {
returnc >= 'A' && c <= 'Z';
 }

/**
 *
 * @param c
 * @return true if character is small Latin letter or false for others
 */
privatestaticbooleanIsSmallLatinLetter(charc) {
returnc >= 'a' && c <= 'z';
 }

/**
 *
 * @deprecated TODO remove main and make JUnit Testing
 */
publicstaticvoidmain(String[] args) {
Scannerinput = newScanner(System.in);
System.out.println("Please enter the message (Latin Alphabet)");
Stringmessage = input.nextLine();
System.out.println(message);
System.out.println("Please enter the shift number");
intshift = input.nextInt() % 26;
System.out.println("(E)ncode or (D)ecode ?");
charchoice = input.next().charAt(0);
switch (choice) {
case'E':
case'e':
System.out.println("ENCODED MESSAGE IS \n" + encode(message, shift)); //send our function to handle
break;
case'D':
case'd':
System.out.println("DECODED MESSAGE IS \n" + decode(message, shift));
 }
 }

}