???????a????????????????????????????????????? a??????????? ????????????????????????a.replace(‘A’?? ‘a’)??? ?????????????????μ?String??????????????????????????????a??String??replace???????????????????

?????????????????????????????????????????′????μ?String???????????????μ????????????????????????????????replace?? substring??toLowerCase???????????????????????????????????????ò????????????
????String ss = "123456";
????System.out.println("ss = " + ss);
????ss.replace('1'?? '0');
????System.out.println("ss = " + ss);
????????????
????ss = 123456
????ss = 123456
????String?????????????
????????????String??????????private final ??????????????????????????????У? value?????????????????????????????????????????value??final???ε??????final?????????????????????????????value?????????? ???罫?????е????λ????????????????“_”?? ?????????????д??????????в?????????????????????????????????value????????????????????????????顣
???????????????????????г????? ?????÷??? ????????String?????е?value????? ??????????????value???????????????????????????
????public static void testReflection() throws Exception {
????//?????????"Hello World"?? ??????????s
????String s = "Hello World";
????System.out.println("s = " + s); //Hello World
????//???String???е?value???
????Field valueFieldOfString = String.class.getDeclaredField("value");
????//???value???????????
????valueFieldOfString.setAccessible(true);
????//???s???????value??????
????char[] value = (char[]) valueFieldOfString.get(s);
????//???value????????????е??5?????
????value[5] = '_';
????System.out.println("s = " + s);  //Hello_World
????}
?????????????
????s = Hello World
????s = Hello_World
??????????????У?s????????????String???????????????????String????????仯?? ???????????????????????ν??“?????”???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????Car??????????????Wheel??????????Wheel????????????private final ??????????Wheel????????????????? ????????????Car???????