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ffahriffahri
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Creating ciphers and adding Caesar Cipher
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‎ciphers/Caesar.java‎

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/**
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Author : FAHRI YARDIMCI
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A Java implementation of Caesar Cipher.
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/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. /
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**/
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import java.util.Scanner;
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public class Caesar {
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public static String encode (String message,int shift)
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{
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String encoded = "";
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for(int i = 0 ; i<message.length() ;i++)
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{
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int current = message.charAt(i); //using char to shift characters because ascii is in-order latin alphabet
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if(current==32)
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{
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encoded += " ";
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continue;
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}
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else if (current>=65 && current<= 90)
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{
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int numAlphabet = message.charAt(i);
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if(shift + numAlphabet > 90)
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{
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int j = 90 - numAlphabet;
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char nextKey = (char)(65 + (shift - j - 1));
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encoded += nextKey;
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}
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else
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{
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char nextKey = (char)(current + shift);
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encoded += nextKey;
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}
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}
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else if (current>=97 && current <= 122)
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{
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int numAlphabet = message.charAt(i);
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if(shift + numAlphabet > 122)
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{
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int j = 122 - numAlphabet;
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char nextKey = (char)(97 + (shift - j - 1));
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encoded += nextKey;
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}
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else
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{
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char nextKey = (char)(current + shift);
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encoded += nextKey;
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}
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}
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}
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return encoded;
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}
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public static String decode (String message,int shift)
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{
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String decoded = "";
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for(int i = 0 ; i<message.length() ;i++)
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{
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int current = message.charAt(i);
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if(current==32)
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{
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decoded += " ";
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continue;
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}
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else if (current>=65 && current<= 90)
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{
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int numAlphabet = message.charAt(i);
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if(numAlphabet - shift < 65)
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{
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int j = numAlphabet - 65;
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char nextKey = (char)(90 - (shift - j - 1));
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decoded += nextKey;
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}
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else
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{
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char nextKey = (char)(current - shift);
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decoded += nextKey;
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}
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}
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else if (current>=97 && current <= 122)
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{
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int numAlphabet = message.charAt(i);
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if(numAlphabet - shift < 97)
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{
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int j = numAlphabet - 97;
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char nextKey = (char)(122 - (shift - j - 1));
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decoded += nextKey;
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}
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else
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{
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char nextKey = (char)(current - shift);
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decoded += nextKey;
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}
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}
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}
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return decoded;
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}
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public static void main(String[] args)
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{
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Scanner input = new Scanner(System.in);
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System.out.println("Please enter the message (Latin Alphabet)");
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String message = input.nextLine();
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System.out.println(message);
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System.out.println("Please enter the shift number");
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int shift = input.nextInt() % 26;
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System.out.println("(E)ncode or (D)ecode ?");
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char choice = input.next().charAt(0);
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if(choice == 'E' || choice=='e')
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System.out.println("ENCODED MESSAGE IS \n" + encode(message,shift)); //send our function to handle
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if(choice =='D' || choice =='d')
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System.out.println("DECODED MESSAGE IS \n" + decode(message,shift));
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}
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}

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