How to change string to lower case? : <p>Trying to make it so that if the user enters any vowel capitalized, it will return true. So, that's where I added the "letter = letter.toLowerCase();" but it's not working still..</p>

<pre><code>    public static boolean isVowel (String letter) {
        letter = letter.toLowerCase();
        if (letter == "a" || letter == "e" || letter == "i" || letter == "o" || letter == "u" ) {
            return true;

        } else {
            return false;
        }
    }
</code></pre>
