where (and what) is the error - java cipher

Question

i am making a cipher, and for some reason it gives me these errors after i input the text:

enter string to be encrypted: 
hello world
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 11
    at chipher.cipher.encrypt(cipher.java:21)
    at chipher.cipher.main(cipher.java:9)

this is my code:

package chipher;
import java.util.Scanner;
public class cipher {
public static int x;
public static int y;
public static Scanner jon = new Scanner(System.in);
    public static void main(String[] args) {
        System.out.println("enter string to be encrypted: ");
        encrypt(jon.nextLine());
        }


public static void encrypt(String tocipher){
    double lngth = tocipher.length();
    tocipher.toLowerCase();
    char[] mynamechars = tocipher.toCharArray();
    char[] alphabet = new char[]{'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'};
for(int i = 0; i<lngth;)
    for(int x = 0; x<26;){
        y = x + 1;
if(mynamechars[i] == alphabet[x]){
    mynamechars[i] = alphabet[y];
}
i++;
x++;
}
    String text = String.valueOf(mynamechars);
    System.out.println(text);
}
}

i don't know what is going on and i am just learning java so it may be something basic, so just bear with me here.

Answer 1

You are doing

mynamechars[i]

upto 25 th index and it seems the input you entered is just 10 character long

Answer 2

You've got two errors. Your first one is due to the way you wrote the for loops and your lack of indentation:

for (int i = 0; i < lngth;) {
    for (int x = 0; x < 26;) {
        y = x + 1;

        if (mynamechars[i] == alphabet[x]) {
            mynamechars[i] = alphabet[y];
        }

        i++;
        x++;
    }

    String text = String.valueOf(mynamechars);
    System.out.println(text);
}

You increment i in the inner loop along with x . You should be incrementing it outside of that loop:

for (int i = 0; i < lngth; i++) {
    for (int x = 0; x < 26; x++) {
        y = x + 1;

        if (mynamechars[i] == alphabet[x]) {
            mynamechars[i] = alphabet[y];
        }
    }

    String text = String.valueOf(mynamechars);
    System.out.println(text);
}

Then there's the problem with y .

x ranges from 0 to 25 , so y will range from 1 to 26 . alphabet doesn't have an element with an index of 26 (that's the 27 ^th letter), which causes your error.

You either have to check for that case manually:

if (mynamechars[i] == alphabet[x]) {
    if (y == 26) {
        y = 0;
    }

    mynamechars[i] = alphabet[y];
}

Or get rid of y completely and use the modulo operator to wrap around to the beginning:

if (mynamechars[i] == alphabet[x]) {
    mynamechars[i] = alphabet[(x + 1) % alphabet.length];
}

Answer 3

Add a System.out.println above y = x + 1; and you should get the meaning of the exception :)