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117 lines (111 loc) · 2.69 KB
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/**
Author : FAHRI YARDIMCI
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. /
**/
import java.util.Scanner;
public class Caesar {
public static String encode (String message,int shift)
{
String encoded = "";
for(int i = 0 ; i<message.length() ;i++)
{
int current = message.charAt(i); //using char to shift characters because ascii is in-order latin alphabet
if(current==32)
{
encoded += " ";
continue;
}
else if (current>=65 && current<= 90)
{
int numAlphabet = message.charAt(i);
if(shift + numAlphabet > 90)
{
int j = 90 - numAlphabet;
char nextKey = (char)(65 + (shift - j - 1));
encoded += nextKey;
}
else
{
char nextKey = (char)(current + shift);
encoded += nextKey;
}
}
else if (current>=97 && current <= 122)
{
int numAlphabet = message.charAt(i);
if(shift + numAlphabet > 122)
{
int j = 122 - numAlphabet;
char nextKey = (char)(97 + (shift - j - 1));
encoded += nextKey;
}
else
{
char nextKey = (char)(current + shift);
encoded += nextKey;
}
}
}
return encoded;
}
public static String decode (String message,int shift)
{
String decoded = "";
for(int i = 0 ; i<message.length() ;i++)
{
int current = message.charAt(i);
if(current==32)
{
decoded += " ";
continue;
}
else if (current>=65 && current<= 90)
{
int numAlphabet = message.charAt(i);
if(numAlphabet - shift < 65)
{
int j = numAlphabet - 65;
char nextKey = (char)(90 - (shift - j - 1));
decoded += nextKey;
}
else
{
char nextKey = (char)(current - shift);
decoded += nextKey;
}
}
else if (current>=97 && current <= 122)
{
int numAlphabet = message.charAt(i);
if(numAlphabet - shift < 97)
{
int j = numAlphabet - 97;
char nextKey = (char)(122 - (shift - j - 1));
decoded += nextKey;
}
else
{
char nextKey = (char)(current - shift);
decoded += nextKey;
}
}
}
return decoded;
}
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
System.out.println("Please enter the message (Latin Alphabet)");
String message = input.nextLine();
System.out.println(message);
System.out.println("Please enter the shift number");
int shift = input.nextInt() % 26;
System.out.println("(E)ncode or (D)ecode ?");
char choice = input.next().charAt(0);
if(choice == 'E' || choice=='e')
System.out.println("ENCODED MESSAGE IS \n" + encode(message,shift)); //send our function to handle
if(choice =='D' || choice =='d')
System.out.println("DECODED MESSAGE IS \n" + decode(message,shift));
}
}