-1 >>> 32 结果为何是 -1? - V2EX
Maxi
V2EX    Java

-1 >>> 32 结果为何是 -1?

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  •   Maxi Oct 12, 2015 4618 views
    This topic created in 3870 days ago, the information mentioned may be changed or developed.
    版本是 jdk8u60, 求指教.
    11 replies    2015-10-16 09:17:43 +08:00
    jwk345
        1
    jwk345  
       Oct 12, 2015 via iPhone   1
    int 是 32 位,向右移 n 位, n 会换算成 n mod 32 ,相当于-1>>>0
    raptium
        2
    raptium  
       Oct 12, 2015   1
    因为其实没有移,左边是 int 的话,右边只看最低 5 bit
    左边是 long 右边看 6 bit
    32 的话,正好是 100000 ,最低 5 个 bit 全是 0
    Maxi
        3
    Maxi  
    OP
       Oct 12, 2015
    多谢二位 @jamesxu @raptium
    firemiles
        4
    firemiles  
       Oct 13, 2015   1
    各位都没说到点子上吧,-1 右移任何位数都是-1 ,因为-1 右移后高位补上的是 1 ,所以-1 补码值不会变,一直是-1
    coderHuang
        5
    coderHuang  
       Oct 13, 2015
    @firemiles 这是算术右移还是逻辑右移?
    zealot0630
        6
    zealot0630  
       Oct 13, 2015
    面试题的话 @jamesxu @raptium 已经可以回家了
    zealot0630
        7
    zealot0630  
       Oct 13, 2015
    @firemiles 留下来参加下一轮面试
    future0906
        8
    future0906  
       Oct 13, 2015
    @firemiles

    误认子弟就是你,哈哈。不熟 Java ,特意去查了,>>>是逻辑右移,不补符号的。

    话说, Java 这样子优化真的没问题?
    firemiles
        9
    firemiles  
       Oct 13, 2015
    @future0906 不好意思, java 不熟,不知道还有这么个逻辑右移符号,以为就是普通的算术右移>>,有点误人子弟了。但是 java 把逻辑右移做成这种效果是想做成循环逻辑右移吗?
    firemiles
        11
    firemiles  
       Oct 16, 2015
    @jamesxu 高级语言用底层语言特性真是坑,用移位操作还是 c 比较清楚简单。
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