Ceasar cipher java code

I have created a code for a caesar cipher with the shift being 25. My code is not encoding the first half of the alphabet, but it is encoding the second half.

I don't know why?

For example, if I try to encode "abcdefghijklmnopqrstuvwxyz", it comes out as "abcdefghijklmmlkjihgfedcba". Only the second half of the alphabet is encoded.

Here is the code:

import java.util.Scanner;
public class Project1

public static void main(String args)

//creating alphabet and coded alphabet arrays
char alphabet = 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',' ';
char codedAlphabet = 'z','y','x','w','v','u','t','s','r','q','p','o','n','m','l','k','j','i','h','g','f','e','d','c','b','a',' ';

//prompting user for encoding or decoding, and for the message
Scanner scan = new Scanner(System.in);
System.out.println("Enter the message: ");
String s = scan.nextLine();
s.toLowerCase();
StringBuffer message = new StringBuffer( s );

Scanner input = new Scanner(System.in);
System.out.println("Enter 1 to encode message, 2 to decode message: ");
int choice = input.nextInt();
if(choice == 1)
encode(message, alphabet, codedAlphabet);
System.out.println(message);
else if(choice == 2)




//method for encoding
public static void encode(StringBuffer message, char a, char b)
for(int i = 0; i<message.length(); i++)
for(int j = 0; j<a.length; j++)
if( message.charAt(i) == a[j])
message.setCharAt(i, b[j]);








break;

message.setCharAt(i, b[j]);

s.toLowercase();

2 Answers
2

Your check for finding the right character is correct. But when you replace the character you have to break that inner loop. Otherwise you keep replacing the same character position more than once if the selected encryption pairing fits. In this case you replace your first character a to z, which is correct, but then replace this new character z again (back to a), which is wrong.

a

z

z

a

public static void encode(StringBuffer message, char a, char b)
for(int i = 0; i<message.length(); i++)
for(int j = 0; j<a.length; j++)
if( message.charAt(i) == a[j])
message.setCharAt(i, b[j]);
// we found the character and replaced it, we
// are done with this position, get to the next "i"
break;






According to your question code, I think this will be the answer.

public static void encode(StringBuffer message, char a, char b)
for(int i = 0; i<message.length(); i++)
for(int j = 0; j<a.length; j++)
if( message.charAt(i) == a[j])
message.setCharAt(i, b[j]);
break;





public static void decode(StringBuffer message, char a, char b)
for(int i = 0; i<message.length(); i++)
for(int j = 0; j<a.length; j++)
if( message.charAt(i) == b[j])
message.setCharAt(i, a[j]);
break;






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