Question

So I’m fairly new to programming, and I’m working on a simple practice program that finds a letters order in the alphabet. This should have been pretty easy…but for some reason I get a StringIndexOutOfBoundsException when I add a while loop. So the program does do what it should the first time…but will not allow me to test again with out re-running the program. I tested the while loop with nothing but a simple print statement inside and it worked, so I’m confused as to why the while loop isn’t working with my alphabet program.

Any help would be greatly appreciated
thanks!

import java.io.*;
public class test {


    public static void main(String[] args) throws IOException 
    {
        BufferedReader in;
        in = new BufferedReader (new InputStreamReader (System.in));
        boolean again=true;
        String response;

        while (again)
        {

            System.out.println("Enter a letter to find it's order in the alphabet");

            char theLetter = (char) in.read();

            System.out.println(theLetter + " is the " + convertLetter(theLetter) + "th letter of the alphabet");

            System.out.println("want to play again?");

            response = in.readLine();

            if (response.charAt(0)=='n')
            {
                again=false;
            }
        }

        System.out.println("end program");
    }


    public static int convertLetter(char TheLetter)
    {
        //number value 'a'=97
        //number value 'b'=98
        //number value 'c'=99

        //subtracting 'a' from any other number will reveal how many places away that number is from the start
        //thus finding it's chronological place in the alphabet

        int NumberValue= (int)TheLetter;
        int a = 'a';

        int CalulateOrder = (NumberValue - a) + 1; 

        return CalulateOrder;

    }
}

Answer 1

When you hit enter for the original char, that newline is still in the buffer since you only call read() and only get 1 character, leaving the newline in the buffer from hitting enter. So when you call readLine it simply hits that newline and returns an empty string.

You can test this by typing something with more than one character when it first asks you for a character, and it will go for a second loop since the readLine will return a non-empty string.

To fix this change your original read() to readLine() so that it gets the newline caused from you hitting enter, then just grab the first character from the string.

This should fix it:

    import java.io.*;

public class test {

    public static void main(String[] args) throws IOException {
        BufferedReader in;
        in = new BufferedReader (new InputStreamReader (System.in));
        boolean again=true;
        String response;

        while (again) {
            System.out.println("Enter a letter to find it's order in the alphabet");
            response = in.readLine();
            if (response.length() > 0) {
                char theLetter = response.charAt(0);

                System.out.println(theLetter + " is the " + convertLetter(theLetter) + "th letter of the alphabet");
                System.out.println("want to play again?");

                response = in.readLine();
                if (response.length() > 0 && response.charAt(0)=='n') {
                    again=false;
                }
            }
        }
        System.out.println("end program");
    }

    public static int convertLetter(char TheLetter) {
        return (TheLetter - 'a') + 1;
    }

}