string index out of bound exception, String index out of range

Question

So, I was writing a simple program to enter a string and count the total no. of m. So, here's my code

for(int i=0; i<=n; i++)
    {
        if((str.charAt(i)=='m'))
        {
        } else {
            count++;
        }
    }
    System.out.println("The total number of m is "+count);

where n=str.length(); and str is a string which I had taken but there this error which keeps coming

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 14
at java.lang.String.charAt(String.java:646)
at javaapplication.JavaApplication.main(JavaApplication.java:28
Java Result: 1

what's this error and how to remove it?

The count++ should be in the if block, not the else block, since you are trying to count the number of m's. — Debosmit Ray
– Debosmit Ray, Commented Feb 22, 2016 at 10:50

Eran · Accepted Answer · 2015-02-28 03:05:33Z

6

A String of length() == n has valid indices from 0 to n-1;

Change

for(int i=0; i<=n; i++)

to

for(int i=0; i<n; i++)

answered Feb 28, 2015 at 3:05

Eran

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Comments

user3437460 · Accepted Answer · 2015-02-28 03:29:23Z

1

Imagine you have the following array of length 7:

-----------------------------
| 0 | 1 | 2 | 3 | 4 | 5 | 6 |  <-- Array index
-----------------------------
|10 |20 |30 |40 |50 |60 |70 |  <-- Array values
-----------------------------

A for loop of for(int i=0; i<=n; i++) in this case will loop 8 times iterating from index 0 to 7.

But the array element at index 7 does not exist, hence giving outOfBoundsException.

Where as a for loop of for(int i=0; i<n; i++) will loop 7 times iterating from 0 to 6.

edited Feb 28, 2015 at 3:29

answered Feb 28, 2015 at 3:24

user3437460

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Comments

Amanda Kirk · Accepted Answer · 2015-02-28 03:10:57Z

0

Remember Strings are indexed from 0 to StringName.length() - 1. Since you are iterating through StringName().length -- you are actually going right outside the "bounds" of the string which is causing the error. You need to make sure your indices are correct in your for loop.

answered Feb 28, 2015 at 3:10

Amanda Kirk

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Comments

Nin-ya · Accepted Answer · 2015-02-28 03:13:25Z

0

Characters in String variable start at 0 index.

Also if you want to count the total appearance of small letter m, move your count++ to your if block statement.

 n=str.length() - 1;
    for(int i=0; i<=n; i++)
        {
            if((str.charAt(i)=='m'))
            {
                  count++;
            }
        }
        System.out.println("The total number of m is "+count);

answered Feb 28, 2015 at 3:13

Nin-ya

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Comments

MaxDevelop · Accepted Answer · 2015-02-28 12:51:33Z

0

charat works with index(works from to n-1), but in your for you get to condition where you have i=n, in this case charat throws exception because it does not have that index in array

answered Feb 28, 2015 at 12:51

MaxDevelop

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