<?php
 
class UtilString
{
    public function stringToCamelCase($string, $character = null)
    {
    	$re = $character == null ? '/^([a-zA-Z])/' : '/(?:^|' . $character . ')([a-zA-Z])/';
        return preg_replace_callback($re, array('UtilString', 'removeCharacterAndCapitalize'), $string);
    }
 
    private function removeCharacterAndCapitalize($matches)
    {
        return strtoupper($matches[1]);
    }
}
 
$str1 = 'string_with_separator';
$str2 = 'string';
 
$test1 = (new UtilString())->stringToCamelCase($str1, '_'); 
$test2 = (new UtilString())->stringToCamelCase($str2);
echo "$test1\n$test2";

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