exception in thread main java.lang.StringIndexOutOfBoundsException

Question

I' m kind of new to Java, and for homework I got this exercise:

write a java program which can take a word from the keyboard and show it reversed ("hello" --> "olleh")

And this is how I wrote the program

import java.util.*;
import java.lang.*;
public class Inverti {
     public static void main(String[] args) {
     System.out.println("digiti una parola o una frase, essa sara' stampata a video alla              rovescia");
     Scanner tastiera = new Scanner(System.in);
     String invertire = tastiera.nextLine();
     for (int i = 0; i < invertire.length();) {
     invertire.replace(invertire.charAt(i), invertire.charAt(invertire.length() - i));
     i++;
         }
System.out.print(invertire);
}
}

(I'm Italian, so consider that "tastiera" means "keyboard" and "digiti una parola o una frase, essa sarà stampata a video alla rovescia" means "type a word, it will be shown reversed")

The program gets compiled, but then, after typing the word:

exception in thread main java.lang.stringindexoutofboundsexception: string 
    index out of bounds: 6 (if string.length() is 6) or 5 (if string.length() = 5).

I looked for answers to other similar questions before posting, but nothing helped me, sorry if the question' s format maybe isn't right.

The value of i is 0 at the first iteration. So charAt(invertire.length()-i) will throw the exception. — Alexis C.
– Alexis C., Commented Jan 12, 2014 at 14:01
replace returns a new String, you should assign the result. — Maroun
– Maroun, Commented Jan 12, 2014 at 14:04
You should always indicate the specific line that was flagged in the exception traceback. (Not that it's hard to figure out here.) — Hot Licks
– Hot Licks, Commented Jan 12, 2014 at 14:05
Understand that in Java a String object is immutable, meaning that any manipulation you do on a String (such as replace) does not modify THAT string but instead returns a new String which you must assign somewhere. — Hot Licks
– Hot Licks, Commented Jan 12, 2014 at 14:07

Maroun · Accepted Answer · 2014-01-12 14:51:07Z

1

In case your line is 6 length long that means the range of possibilities are [0, 5].
Then if we take i as 0 and invertire as 6 will get the following evaluation:

invertire.charAt(6 - 0)

The result is of course invertire.charAt(6) that doesn't appears in the range, and it's what causing the exception.

Fix:

invertire.charAt(invertire.length() - i - 1)

edited Jan 12, 2014 at 14:51

Maroun

96.3k30 gold badges195 silver badges249 bronze badges

answered Jan 12, 2014 at 14:09

Orel Eraki

12.2k4 gold badges31 silver badges38 bronze badges

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

Comments

Ashish · Accepted Answer · 2014-01-12 14:12:46Z

0

I'd do something like this:

Scanner tastiera = new Scanner(System.in);
String input = tastiera.nextLine();
StringBuilder inverse = new StringBuilder();
for (int i = 0; i < input.length();i++) {
inverse.append(input.charAt(input.length()-1-i));
}
System.out.print(inverse);

answered Jan 12, 2014 at 14:12

Ashish

1,1213 gold badges15 silver badges25 bronze badges

2 Comments

Alexis C. Over a year ago

If you're using a StringBuilder, why don't you simply do String inverse = new StringBuilder(input).reverse().toString(); ?

Ashish Over a year ago

yes thats the easiest way to achieve String reversal. I was not trying to take a short cut here.

Collectives™ on Stack Overflow

exception in thread main java.lang.StringIndexOutOfBoundsException

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related