Getting error while taking typecasted number as index in array In Java

Question

public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        String table[] = { " ", ".+@$", "abc", "def", "ghi", "jkl" , "mno", "pqrs" , "tuv", "wxyz" };
        String str = sc.nextLine();
        int cn =(int)str.charAt(0);
        System.out.println(table[cn]);
    }
}

For input 12 this code is giving me Error as :- Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 49 at Main.main(Main.java:8)

can someone explain me why is this error coming and how to remove this error?

Answer 1

.charAt() method returns a character and when you parse it into int, it will give you the ascii value of that character.

For example, if you enter 12, str.charAt(0) will return '1' and converting this character into int will give you 49 (ascii value for character 1) and index number 49 is out of bounds for the table array.

Solution:

You could convert the character returned by .charAt() method into String by passing the return value of str.charAt(0) as an argument to String.valueOf() and then parse that String into an int type by passing the return value of String.valueOf() as an argument to Integer.parseInt().

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String table[] = { " ", ".+@$", "abc", "def", "ghi", "jkl" , "mno", "pqrs" , "tuv", "wxyz" };
    String str = sc.nextLine();
    
    int cn = Integer.parseInt(String.valueOf(str.charAt(0)));   // <-----
    
    System.out.println(table[cn]);
}

You could also use + operator to concatenate str.charAt(0) with an empty String and then pass the resulting String to Integer.parseInt().

int cn = Integer.parseInt("" + str.charAt(0));