public static String join(CharSequence delimiter, CharSequence... elements) {
        StringBuilder builder = new StringBuilder();

        boolean first = true;

        for (CharSequence element : elements) {
            if(first) {
                first = false;
            } else {
                builder.append(delimiter);
            }
            builder.append(element);
        }

        return builder.toString();
    }
@Test
    public void testJoin(){
        assertEquals(
            "Oracle,PostgreSQL,MySQL,SQL Server",
            StringUtils.join(",", "Oracle", "PostgreSQL", "MySQL", "SQL Server")
        );
    }