ROT-13 function in java?

Question

Is there already a rot13() and unrot13() implementation as part of one of the standard Java libraries? Or do I have to write it myself and "reinvent the wheel"?

It might look something like this:

int rot13 ( int c ) { 
  if ( (c >= 'A') && (c <= 'Z') ) 
    c=(((c-'A')+13)%26)+'A';

  if ( (c >= 'a') && (c <= 'z') )
    c=(((c-'a')+13)%26)+'a';

  return c; 
}

Answer 1

I don't think it's part of Java by default, but here's an example of how you can implement it;

public class Rot13 { 

    public static void main(String[] args) {
        String s = args[0];
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if       (c >= 'a' && c <= 'm') c += 13;
            else if  (c >= 'A' && c <= 'M') c += 13;
            else if  (c >= 'n' && c <= 'z') c -= 13;
            else if  (c >= 'N' && c <= 'Z') c -= 13;
            System.out.print(c);
        }
        System.out.println();
    }

}

Source: http://introcs.cs.princeton.edu/java/31datatype/Rot13.java.html

Answer 2

Might as well contribute my function to save other developers the valuable seconds

public static String rot13(String input) {
   StringBuilder sb = new StringBuilder();
   for (int i = 0; i < input.length(); i++) {
       char c = input.charAt(i);
       if       (c >= 'a' && c <= 'm') c += 13;
       else if  (c >= 'A' && c <= 'M') c += 13;
       else if  (c >= 'n' && c <= 'z') c -= 13;
       else if  (c >= 'N' && c <= 'Z') c -= 13;
       sb.append(c);
   }
   return sb.toString();
}

Answer 3

Here is my solution to shift chars in a string.

public static void main(String[] args) {
    String input = "melike";
    int shiftCount = 13;
    char[] encryptedChars = encryptedChars(shiftCount);
    System.out.println(new String(encryptedChars));
    char[] decryptedChars = decryptedChars(shiftCount);
    System.out.println(new String(decryptedChars));
    String encrypted = encrypt(input, shiftCount);
    System.out.println(encrypted);
    String decrypted = decrypt(encrypted, shiftCount);
    System.out.println(decrypted);
    System.out.println(input.equals(decrypted));
}

private static String decrypt(String input, int shiftCount) {
    char[] decryptedChars = decryptedChars(shiftCount);
    char[] chars = input.toCharArray();
    char[] newChars = new char[chars.length];
    for (int i = 0; i < chars.length; i++) {
        int diff = chars[i] - 'a';
        newChars[i] = decryptedChars[diff];
    }
    return new String(newChars);
}

private static String encrypt(String input, int shiftCount) {
    char[] encryptedChars = encryptedChars(shiftCount);
    char[] chars = input.toCharArray();
    char[] newChars = new char[chars.length];
    for (int i = 0; i < chars.length; i++) {
        int diff = chars[i] - 'a';
        newChars[i] = encryptedChars[diff];
    }
    return new String(newChars);
}

private static char[] encryptedChars(int shiftCount) {
    char[] newChars = new char[26];
    for (int i = 0; i < 26; i++) {
        newChars[i] = (char) ('a' + (i + shiftCount) % 26);
    }
    return newChars;
}

private static char[] decryptedChars(int shiftCount) {
    char[] newChars = new char[26];
    for (int i = 0; i < 26; i++) {
        newChars[i] = (char) ('a' + (i - shiftCount + 26) % 26);
    }
    return newChars;
}