????byte????int???????????
????1??????????????
????????????????????????
???????????????????????????????int i = (int) aByte??
???????磺??aByte=0xff????????-1??????????int??i?0xffffffff????????-1??
????2???????????и???λ????3????????????0???
??????ó???????????????
?????????????λ??????int i = aByte & 0xff??
???????磺??aByte=0xff??????int??i?0x000000ff??