String index out of bounds? (Java, substring loop)

Question

This program I'm making for a COSC course isn't compiling right, I keep getting the error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 2

at java.lang.String.substring(String.java:1765) at VowelCount.main(VowelCount.java:13)

Here's my code:

import java.util.Scanner;

public class VowelCount {
 public static void main(String[] args) {
  int a = 0, e = 0, i = 0, o = 0, u = 0, count = 0;
  String input, letter;
  Scanner scan = new Scanner (System.in);

  System.out.println ("Please enter a string: ");
  input = scan.nextLine();

  while (count <= input.length() ) {
   letter = input.substring(count, (count + 1));

   if (letter == "a") {
    a++; }
   if (letter == "e") {
    e++; }
   if (letter == "i") {
    i++; }
   if (letter == "o") {
    o++; }
   if (letter == "u") {
    u++; }

   count++;

  }
  System.out.println ("There are " + a + " a's.");
  System.out.println ("There are " + e + " e's.");
  System.out.println ("There are " + i + " i's.");
  System.out.println ("There are " + o + " o's.");
  System.out.println ("There are " + u + " u's.");
 }
}

To my knowledge this should work, but why doesn't it? Any help would be great. Thank you!

Vincent Ramdhanie · Accepted Answer · 2009-10-15 01:36:30Z

5

You may need to take out the = in the line

while (count <= input.length() ) {

and make it

while (count < input.length() ) {

because it is causing the substring to read beyond the length of the string.

=============== But I'll add a few extra bits of advice even though its not asked for:

do not use == to compare strings, use

letter.equals("a")

instead. Or even better, try using

char c = input.charAt(count);

to get the current character then compare like this:

c == 'a'

answered Oct 15, 2009 at 1:36

Vincent Ramdhanie

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Comments

bcat · Accepted Answer · 2009-10-15 01:38:13Z

0

I think your loop condition should be count < input.length. Right now, the last iteration runs with count == length, so your substring call is given a start index after the last character in the string, which is illegal. These type of boundary errors are very common when writing such loops, so it's always good to double- and triple-check your loop conditions when you encounter a bug like this.

Also, comparing strings with the == operator usually won't do what you want. That compares whether or not the two variables reference the same object. Instead, you want to test string1.equals(string2), which compares the contents of the two strings.

answered Oct 15, 2009 at 1:38

bcat

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Comments

mauris · Accepted Answer · 2009-10-15 01:42:49Z

0

Removing the equal sign should fix that.

while (count < input.length()) {

and since you want to get a single character, you should do this:

substr(count,1)

because the 2nd parameter is actually length, not index.

edited Oct 15, 2009 at 1:42

answered Oct 15, 2009 at 1:37

mauris

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2 Comments

Brad Over a year ago

Alright, it compiles! But still doesn't output the right amounts. Test string "aeiou" results in 0, 0, 0, 0, 0..

Vincent Ramdhanie Over a year ago

Do not use == to compare strings as mentioned in other answers

Brad · Accepted Answer · 2009-10-15 01:45:37Z

0

Fixed it with help from everyone, and especially Vincent. Thank you! Runs wonderfully.

import java.util.Scanner;

public class VowelCount {
    public static void main(String[] args) {
        int a = 0, e = 0, i = 0, o = 0, u = 0, count = 0;
        String input;
        char letter;

        Scanner scan = new Scanner (System.in);

        System.out.print ("Please enter a string: ");
        input = scan.nextLine();

        while (count < input.length() ) {
            letter = input.charAt (count);

            if (letter == 'a')
                a++; 
            if (letter == 'e') 
                e++; 
            if (letter == 'i') 
                i++; 
            if (letter == 'o') 
                o++; 
            if (letter == 'u') 
                u++; 

            count++;

        }
        System.out.println ("There are " + a + " a's.");
        System.out.println ("There are " + e + " e's.");
        System.out.println ("There are " + i + " i's.");
        System.out.println ("There are " + o + " o's.");
        System.out.println ("There are " + u + " u's.");
    }
}

answered Oct 15, 2009 at 1:45

Brad

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4 Comments

pstanton Over a year ago

you can use a for loop to tidy it up even further: - for(int count = 0; count < input.length(); count++)

WilQu Over a year ago

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post.

meda Over a year ago

@WilQu did you read this question? it's the OP posting the working solution. how should this be a comment?

WilQu Over a year ago

@meda I see this as a comment only saying that the other answers worked. It does not add anything to the existing answers.

Arsalan Khan · Accepted Answer · 2017-04-20 11:48:10Z

0

Before loop,try below

if(input.length()>0){
//you code
}

answered Apr 20, 2017 at 11:48

Arsalan Khan

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