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; 
}

@BNL I personally prefer rot104. Requires a dedicated coprocessor though — Chris Thompson, Jan 24 '12 at 02:26
@BNL LOL who said it's for security purposes? See [this](http://stackoverflow.com/questions/3928903/what-are-some-practical-applications-of-the-rot13-algorithm) — Regex Rookie, Jan 24 '12 at 02:32
By the way, rot13 is its own inverse, so you don't actually need an "unrot13" method. — Brian Rogers, Jan 24 '12 at 07:05

score 29 · Answer 1 · answered Jul 01 '13 at 02:42

29

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();
}

answered Jul 01 '13 at 02:42

georgiecasey

21,793
11
65
74

Thanks for taking the time to put this into a method. – james.garriss Dec 17 '15 at 17:09
3

Did you also copy http://introcs.cs.princeton.edu/java/31datatype/Rot13.java.html ? – Christoffer Hammarström Dec 17 '15 at 17:13
how can I add numbers to this function? 0-9 i want to rotate a-zA-Z0-9, kind of a caseSensitive rot18 – Hamid Habibi Jun 15 '22 at 05:28

score 21 · Accepted Answer · edited Feb 11 '14 at 15:14

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

score 1 · Answer 3 · answered Sep 23 '21 at 09:34

private final static List<String> upperAlphabets = Arrays.asList(
        "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");
private final static List<String> lowerAlphabets = Arrays.asList(
        "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");

 private static void rot(int toSkip, String value) {
        StringBuilder sb = new StringBuilder();
        int pos = 0, newPos = 0;
        boolean upper;
        for (char c : value.toCharArray()) {
            pos = upperAlphabets.indexOf(String.valueOf(c));
            if (pos == -1) {
                pos = lowerAlphabets.indexOf(String.valueOf(c));
                upper = false;
            } else {
                upper = true;
            }

            if (pos + toSkip > 25) {
                newPos = (pos + toSkip) % 26;
            } else {
                newPos = pos + toSkip;
            }

            if (upper) {
                sb.append(upperAlphabets.get(newPos));
            } else {
                sb.append(lowerAlphabets.get(newPos));
            }
        }
        System.out.println(sb);
    }

This is not only about rot13, this can do rot100 or rot1213 anything depending upon what value you are passing and the most important thing is that both list of upper case and lower case alphabets are must.

score 0 · Answer 4 · answered May 24 '23 at 02:22

Sometimes inputs might have special characters, so it's better to include them.

    String input = "Do you have any cat pictures?";
    StringBuilder op = new StringBuilder();

    for (int i = 0; i < input.length(); i++) {
        char c = input.charAt(i);

        if (c == ' ') {
            op.append(" ");
        } else if (c >= 'a' && c <= 'z') {
            if (c > 'm') c -= 13;
            else c += 13;
            op.append(c);
        } else if (c >= 'A' && c <= 'Z') {
            if (c > 'M') c -= 13;
            else c += 13;
            op.append(c);
        } else {
            op.append(c);
        }
    }

score -1 · Answer 5 · answered Aug 26 '21 at 08:31

-1

you be doing like dis:

pblic class Rot13 {

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

answered Aug 26 '21 at 08:31

Mr Good

1

Why copy the accepted message and make it worse by breaking the formatting and deleting some characters? What's the point of that? – Generous Badger Aug 26 '21 at 08:39

ROT-13 function in java?

5 Answers5

Linked

Related