Java- shifting a ROT13 string

Question

I want to shift a ROT13 string by a user-inputted amount. This is the sample output:

Enter your text to encrypt (!!! to quit): abcdefghijklmnopqrstuvwxyz

Enter amount to shift text by: 3

ORIGINAL: abcdefghijklmnopqrstuvwxyz

ENCRYPTED: defghijklmnopqrstuvwxyzabc

The user MUST provide a shift value between 0 and 26. If the user goes out of this range, the program should force the user to enter a valid value:

Enter your text to encrypt (!!! to quit): the quick brown fox jumped over the lazy dog
Enter amount to shift text by: -3
ERROR! Shift must be non-negative!
Enter amount to shift text by: 33
ERROR! Shift must be no more than 26!
Enter amount to shift text by: 2

Enter your text to encrypt (!!! to quit): !!! Goodbye!

This is my code that I have written:

import java.util.Scanner;

public class Lab08b 
{

public static void main(String[] args)
{
    Scanner sc = new Scanner (System.in);
    String input = getText(sc);
    int shift = getShift(sc);
    if (input.equals("!!!"))
    {
        System.out.println("Goodbye!");
    }

    while (!input.equals("!!!"))
    {
        String encoded = rot13(input);
        shiftMessage(input, shift);
        displayResults(input, encoded);
        input = getText(sc);
        if (input.equals("!!!"))
        {
            System.out.println("Goodbye!");
        }
    }


}
private static int getShift (Scanner inScanner)
{
    System.out.print("Enter amount to shift text by: ");
    int shift = inScanner.nextInt();

    if (shift < 0)
    {
        System.out.println("ERROR! Shift must be non-negative!");
        System.out.print("Enter amount to shift text by: ");
        shift = inScanner.nextInt();
    }
    else if (shift > 26)
    {
        System.out.println("ERROR! Shift must be non-negative!");
        System.out.print("Enter amount to shift text by: ");
        shift = inScanner.nextInt();
    }
    return shift;
}

private static String getText(Scanner inScanner)
{
    System.out.print("Enter your text to encrypt (!!! to quit): ");
    String original = inScanner.nextLine();

    while (original.equals(""))
    {
        System.out.println("ERROR! String must not be empty!");
        System.out.print("Enter your text to encrypt (!!! to quit): ");
        original = inScanner.nextLine();
    }
    return original;
}


private static String rot13(String input)
{
    String str = "";

    for (int i = 0; i < input.length(); i++)
    {
        char ch = input.charAt(i);
        if (ch >= 'A' && ch <= 'Z')
        {
            ch = (char) (ch + 13);
            if (ch > 'Z')
            {
                ch = (char)(ch - 26);
            }
        }
        else if (ch >= 'a' && ch <= 'z')
        {
            ch = (char)(ch + 13);
            if (ch > 'z')
            {
                ch = (char)(ch - 26);
            }
        }
        str = str + ch;
    }
    return str;
}

private static void displayResults(String inText, String encText)
{
    System.out.print("+");
    for (int i = 13 + encText.length(); i > 0; i--)
    {
        System.out.print("-");
    }
    System.out.println("+");

    System.out.println("| ORIGINAL:  " + inText + " |");
    System.out.println("| ENCRYPTED: " + encText + " |");

    System.out.print("+");
    for(int i = 13 + encText.length(); i > 0; i--){
        System.out.print("-");
    }
    System.out.println("+");
}

private static String shiftMessage(String input, int n)
{
    for (int i = 0; i < input.length(); i++)
    {
        input = input.charAt(input.length()- n) + input.substring(0,input.length());
    }
    return input;
}

}

UPDATE: THIS CODE IS HOW I HAVE PROGRESSED. The actual shifting still does not work http://pastebin.com/v2T1fxEj

I have it printing out the ROT13 encryption and everything, I just don't know how to shift it.

also, when I try to add the "Enter amount to shift by" in the main method below String input = getText(sc), I just end up getting this:

Enter your text to encrypt (!!! to quit): ERROR! String must not be empty!
Enter your text to encrypt (!!! to quit):

I am not supposed to get that

Don't use pastebin. Show your code in the question please. This question will not be useful to others if they come along later and the link is broken. — nhouser9, Oct 20 '16 at 23:14
Possible duplicate of [ROT-13 function in java?](http://stackoverflow.com/questions/8981296/rot-13-function-in-java) — Charles, Oct 20 '16 at 23:20
Its not a duplicate. I have completed the actual ROT. I cannot find how to do the shifting though. — ConfusedCoder, Oct 20 '16 at 23:22
I just added a new method to get the shift amount, but I still get that problem where is says ERROR! — ConfusedCoder, Oct 20 '16 at 23:30
based on the example you would use substring. Assuming shift == 3, here is how you would write it encoded.substring(3) + encoded.substring(0, 3) — Sanj, Oct 20 '16 at 23:34
No, I get the actual encryption, and then it follows with Enter your text to encrypt (!!! to quit): ERROR! String must not be empty! Enter your text to encrypt (!!! to quit): — ConfusedCoder, Oct 20 '16 at 23:41
@ConfusedCoder: Replace 3 with whatever is the shift value. Just validate the length of encrypted string before shifting. — Sanj, Oct 20 '16 at 23:46

Ole V.V. · Accepted Answer · 2016-10-21T11:24:30.900

shiftMessage() is like rot13(), only put in n instead of 13:

private static String shiftMessage(String input, int n) {
    String str = "";

    for (int i = 0; i < input.length(); i++)
    {
        char ch = input.charAt(i);
        if (ch >= 'A' && ch <= 'Z')
        {
            ch = (char) (ch + n);
            if (ch > 'Z')
            {
                ch = (char)(ch - 26);
            }
        }
        else if (ch >= 'a' && ch <= 'z')
        {
            ch = (char)(ch + n);
            if (ch > 'z')
            {
                ch = (char)(ch - 26);
            }
        }
        str = str + ch;
    }
    return str;
}

Now when I call shiftMessage() instead of rot13() from main(), I can:

Enter your text to encrypt (!!! to quit): abcdefghijklmnopqrstuvwxyz
Enter amount to shift text by: 1
+---------------------------------------+
| ORIGINAL:  abcdefghijklmnopqrstuvwxyz |
| ENCRYPTED: bcdefghijklmnopqrstuvwxyza |
+---------------------------------------+

Other issues:

ERROR! String must not be empty!, which you mention, is a classic with Scanner.nextInt(). nextInt() only reads the number, not the newline following it. So when you subsequently do inScanner.nextLine(), it reads the newline and returns an empty string. I believe the solution is to call nextLine() after nextInt() to get rid of the newline.

Last, you cannot know in advance that the user will only type an incorrect shift amount once. I can do:

Enter your text to encrypt (!!! to quit): abc
Enter amount to shift text by: -3
ERROR! Shift must be non-negative!
Enter amount to shift text by: -3
+----------------+
| ORIGINAL:  abc |
| ENCRYPTED: ^_` |
+----------------+

Hey, thanks for the help! However, whenever I tried to add nextLine(), eclipse complained and said that it can't invoke nextLine() on the primitive type int. Is there another fix for that? For the last thing you said, I realized that I can fix that by just using a while loop, I was using an if-statement, so it would mess up the encryption if i was out of bounds more than once — ConfusedCoder, Oct 21 '16 at 00:35
I’m not an expert on `Scanner`. The message sounds like you were trying `inScanner.nextInt().nextLine()` or something. Rather try `inScanner.nextLine();` on a separate line. — Ole V.V., Oct 21 '16 at 00:46
Ahhh never mind. I got it. I ended up just changing [nextLine()] in [getText] to just [next()] — ConfusedCoder, Oct 21 '16 at 00:47

Java- shifting a ROT13 string

1 Answers1