ROT13. There are 26 letters in the alphabet. With ROT13, a cipher, we rotate the first 13 with the last 13. This obscures, but does not encrypt, text data.
A String is immutable: it cannot be changed. To modify a String with the ROT13 algorithm in Java we must first convert it to a character array. Then we convert it back to a String.
A method. We introduce an example method. In rot13() we see the character-testing logic. Characters before the middle letter M are rotated backwards, and other are rotated forwards.
Start We pass our character array to the String constructor to convert it back into a String.
Here We rotate a String, and then rotate the rotated string to see if it correctly round-trips (it does).
public class Program {
public static String rot13(String value) {
char[] values = value.toCharArray();
for (int i = 0; i < values.length; i++) {
char letter = values[i];
if (letter >= 'a' && letter <= 'z') {
// Rotate lowercase letters.
if (letter > 'm') {
letter -= 13;
} else {
letter += 13;
}
} else if (letter >= 'A' && letter <= 'Z') {
// Rotate uppercase letters.
if (letter > 'M') {
letter -= 13;
} else {
letter += 13;
}
}
values[i] = letter;
}
// Convert array to a new String.
return new String(values);
}
public static void main(String[] args) {
// Rotate the input string.// ... Then rotate the rotated string.
String input = "Do you have any cat pictures?";
String rot13 = rot13(input);
String roundTrip = rot13(rot13);
System.out.println(input);
System.out.println(rot13);
System.out.println(roundTrip);
}
}Do you have any cat pictures?
Qb lbh unir nal png cvpgherf?
Do you have any cat pictures?
For punctuation and spaces, no changes are made. Most text remains in a recognizable form, so it is easy to detect ROT13. The algorithm is usually just a learning exercise.
Occasionally, if you want to make text not easily read, using ROT13 is helpful. A sophisticated computer user can decode ROT13, but many users are not sophisticated or don't care.
Dot Net Perls is a collection of pages with code examples, which are updated to stay current. Programming is an art, and it can be learned from examples.
Donate to this site to help offset the costs of running the server. Sites like this will cease to exist if there is no financial support for them.
Sam Allen is passionate about computer languages, and he maintains 100% of the material available on this website. He hopes it makes the world a nicer place.