converting character to array index

Question

I am trying to access an array of characters by reading the array index from a String.

public class HelloWorld {

    public static void main(String[] args) {
        //             0123456789
        char[] code = {'A', 'B','C','D','E','F','G','H','I','J'};
        String orig = "0123456789";
        for ( int i=0; i <10; i++) {
            System.out.print(code[orig.charAt(i)]);
        }
    }

}

I was hoping for the output of ABCDEFGHIJ but instead I get a runtime error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 48
    at HelloWorld.main(HelloWorld.java:9)

Have you tried adding breakpoints within your loop to see what the code is actually doing? — Anthony Forloney
– Anthony Forloney, Commented Dec 23, 2014 at 2:55

haley · Accepted Answer · 2014-12-23 02:56:23Z

3

This is because orig.charAt(i) returns a character which is ascii. So '0' is actually the number 48. You can easily fix this by doing:

code[orig.charAt(i) - 48];

answered Dec 23, 2014 at 2:56

haley

1,1757 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

August · Accepted Answer · 2014-12-23 02:58:36Z

1

When you use orig.charAt(i) as the index, the char value gets converted to an int. Each character has a numerical value. '0', for instance, is 48. You can subtract the lowest character value you encounter to get an index in the correct range:

System.out.print(code[orig.charAt(i) - '0']);

answered Dec 23, 2014 at 2:58

August

12.6k3 gold badges38 silver badges53 bronze badges

Comments

Edward J Beckett · Accepted Answer · 2014-12-23 03:13:31Z

1

Just index over the length of the string and get the character of the code array at that index... charAt will give you the literal int value which is obviously not what you want.

public static void main(String[] args) {
        //  0123456789
        char[] code = {'A', 'B','C','D','E','F','G','H','I','J'};
        String orig = "0123456789";
        for ( int i=0; i < orig.length(); i++) {
            System.out.print( code[i] );
        }
    }

edited Dec 23, 2014 at 3:13

answered Dec 23, 2014 at 2:59

Edward J Beckett

5,1402 gold badges43 silver badges41 bronze badges

Comments

23Stinger · Accepted Answer · 2014-12-23 03:29:46Z

1

Since array indexes are int it is automatically converted to an int.
But the int value of the char '0' is 48, hence the message "ArrayIndexOutOfBoundsException".
The below code should do it

System.out.print(code[orig.charAt(i)-48]);

answered Dec 23, 2014 at 3:29

23Stinger

663 bronze badges

Collectives™ on Stack Overflow

converting character to array index

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related