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          Bitwise operators and Shift operators

          位運(yùn)算符與邏輯運(yùn)算符基本相似,不過后者的對象只是表示真和假的二值運(yùn)算,位運(yùn)算符的對象則是二進(jìn)制數(shù)。Java語言中字節(jié)、字符和整數(shù)等都可以轉(zhuǎn)換為二進(jìn)制,所以位運(yùn)算符的對象也可以是它們。常見位運(yùn)算符有:
          按位進(jìn)行與運(yùn)算 : &
          按位進(jìn)行或運(yùn)算 : |
          按位進(jìn)行位異運(yùn)算: ^
          按位進(jìn)行取反運(yùn)算: ~
          按位進(jìn)行循環(huán)左移:<<,運(yùn)算符左側(cè)對象左移由右側(cè)指定的位數(shù),低位補(bǔ)0,最高位拋棄。帶符號的左移位運(yùn)算相當(dāng)于對左操作數(shù)進(jìn)行乘2運(yùn)算。
          按位進(jìn)行循環(huán)右移:>>,運(yùn)算符左側(cè)對象右移由右側(cè)指定的位數(shù),若值為正,在最高位插入0,若值為負(fù),在最高位插入1,即移入的最高位和原最高符號位相同。帶符號的右移位運(yùn)算相當(dāng)于對左邊的運(yùn)算對象進(jìn)行除2運(yùn)算。
          按位進(jìn)行無符號右移:>>>,無論運(yùn)算符左邊的運(yùn)算對象取值正負(fù),都在高位插入0,即移入位始終補(bǔ)0.
          要注意是沒有按位進(jìn)行無符號左移的。位運(yùn)算符的操作數(shù)只能是整數(shù),char,byte,short,
          int和long,進(jìn)行位運(yùn)算時,總是先將字符型值、字節(jié)型值和短整型值轉(zhuǎn)換為整型再進(jìn)行位運(yùn)算。位運(yùn)算符游標(biāo)的操作數(shù)用于指定移動的位數(shù),按規(guī)定其不應(yīng)超過左側(cè)數(shù)的進(jìn)制表示位數(shù)。
          The bitwise operators allow you to manipulate individual bits in an integral primitive data type.Bitwise operators perform Boolean algebra on the corresponding bits in the two arguments to produce the result. The bitwise operators come from C’s low-level orientation, where you often manipulate hardware
          directly and must set the bits in hardware registers. Java was originally designed to be embedded in TV set-top boxes, so this low-level orientation still made sense. However, you probably won’t use the bitwise operators much.
          The bitwise AND operator (&) produces a one in the output bit if both input bits are one; otherwise, it produces a zero.
          The bitwise OR operator (|) produces a one in the output bit if either input bit is a one and produces a zero only if both input bits are zero.
          The bitwise EXCLUSIVE OR, or XOR (^), produces a one in the output bit if one or the other input bit is a one, but not both.
          The bitwise NOT (~, also called the ones complement operator) is a unary operator; it takes only one argument. (All other bitwise operators are binary operators.) Bitwise NOT produces the opposite of the input bit—a one if the input bit is zero, a zero if the input bit is one.

          posted on 2008-05-20 13:22 九寶 閱讀(382) 評論(0)  編輯  收藏 所屬分類: Java Study(JavaThinking4)

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