Java - How to double only Vowels

Question

I am trying to write code that would double all vowels within a string. So if the string is hello, it would return heelloo. This is what I currently have:

public String doubleVowel(String str)
{
    for(int i = 0; i <= str.length() - 1; i++)
    {
        char vowel = str.charAt(i);
        if(vowel == 'a' || vowel == 'e' || vowel == 'i' || vowel == 'o' || vowel == 'u')
        {

        }
    }
}

Answer 1

You can use a regular expression with a single call to String.replaceAll(String, String) and your method might be static because you don't need any instance state (also, don't forget upper case vowels). Something like

public static String doubleVowel(String str) {
    return str.replaceAll("([AaEeIiOoUu])", "$1$1");
}

Where $1 matches the first (only) pattern grouping expressed in ().