public static String lowercaseFirstLetter(String string) {
        if (string == null || string.length() == 0) {
            return string;
        } else {
            return string.substring(0, 1).toLowerCase() + string.substring(1);
        }
    }
@Test
    public void testLowercaseFirstLetter() {
        assertEquals(lowercaseFirstLetter(""), (""));
        assertEquals(lowercaseFirstLetter("A"), ("a"));
        assertEquals(lowercaseFirstLetter("AA"), ("aA"));
        assertEquals(lowercaseFirstLetter("a"), ("a"));
        assertEquals(lowercaseFirstLetter("aB"), ("aB"));
    }