Caesar.java

packagecom.thealgorithms.ciphers;

/**
 * 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 {
privatestaticcharnormalizeShift(finalintshift) {
return (char) (shift % 26);
 }

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

finalcharshiftChar = normalizeShift(shift);

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 += shiftChar;
encoded.append((char) (current > 'Z' ? current - 26 : current)); // 26 = number of latin letters
 } elseif (isSmallLatinLetter(current)) {
current += shiftChar;
encoded.append((char) (current > 'z' ? current - 26 : current)); // 26 = number of latin letters
 } else {
encoded.append(current);
 }
 }
returnencoded.toString();
 }

/**
 * Decrypt message by shifting back every Latin char to previous the ASCII
 * Example : B - 1 -> A
 *
 * @return message
 */
publicStringdecode(StringencryptedMessage, intshift) {
StringBuilderdecoded = newStringBuilder();

finalcharshiftChar = normalizeShift(shift);

finalintlength = encryptedMessage.length();
for (inti = 0; i < length; i++) {
charcurrent = encryptedMessage.charAt(i);
if (isCapitalLatinLetter(current)) {
current -= shiftChar;
decoded.append((char) (current < 'A' ? current + 26 : current)); // 26 = number of latin letters
 } elseif (isSmallLatinLetter(current)) {
current -= shiftChar;
decoded.append((char) (current < 'a' ? current + 26 : current)); // 26 = number of latin letters
 } else {
decoded.append(current);
 }
 }
returndecoded.toString();
 }

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

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

/**
 * @return string array which contains all the possible decoded combination.
 */
publicString[] bruteforce(StringencryptedMessage) {
String[] listOfAllTheAnswers = newString[27];
for (inti = 0; i <= 26; i++) {
listOfAllTheAnswers[i] = decode(encryptedMessage, i);
 }

returnlistOfAllTheAnswers;
 }
}