Duplicate vowels in string
<p>I have to write a method that takes in a String and returns a new 
string that replaces every vowel with two occurrences of 
that vowel.</p>

<p>For example: "hello" would return "heelloo"</p>

<p>I've experimented with my code for hours but I am not getting anything done. Here is my code:</p>

<pre><code>public static String doubleVowel(String str)
{ 
String result = str;
for(int i = 0; i &lt; str.length(); i++)
{
    if((str.charAt(i) == 'a') || 
    (str.charAt(i) == 'e')  ||
    (str.charAt(i) == 'i') || 
    (str.charAt(i) == 'o') ||
    (str.charAt(i) == 'u')) 
    {
        result = result.substring(0, i + 1) + Character.toString(result.charAt(i)) 
        + result.substring(i + 1, result.length());
        i++;
    }
}          
return result;
}
</code></pre>

<p>When the input is "hello", the output is "heelllo"<br/>
When the input is "computer" the output is "coomppuuter"<br/>
When the input is "sweet" the output is "sweeet"<br/></p>

<p>I have racked my brain but to no avail. What is causing the bug in the program, and is there a simpler way to do this?</p>