StringUtil { public static String lowerFirstChar(String s) { if (Character.isLowerCase(s.charAt(0))) { return s; } return (new StringBuilder()).append(Character.toLowerCase(s.charAt(0))).append(s.substring(1)).toString(); } private  StringUtil(); static boolean isNullOrEmpty(String str); static boolean isInteger(String str); static boolean isDouble(String str); static String upFirstChar(String Str); static String lowerFirstChar(String s);  }
@Test public void testLowerFirstChar() { Assert.assertEquals("aA", StringUtil.lowerFirstChar("AA")); Assert.assertEquals("!", StringUtil.lowerFirstChar("!")); }