为什么-1右移1 = -1在Java中？ [英] Why is -1 right shift 1 = -1 in Java?
问题描述
我遇到的问题<一来到href=\"http://stackoverflow.com/questions/20439767/why-is-1-zero-fill-right-shift-1-2147483647-for-integers-in-java\">\"Why为-1补零右转向的Java 1 = 2147483647整数？
我的理解填零的概念，直接从上面的问题的答案移位得很清楚。但是，当我试图找到-1 >> 1，我得到一个完全复杂的答案，我觉得很难理解。
I understood the concept of zero fill right shift perfectly well from the above question's answer. But when I tried to find -1>>1, I am getting a totally complex answer which I felt difficult to understand.
-1 in binary form is as follows: 11111111111111111111111111111111
After flipping the bits, I got: 00000000000000000000000000000000
Upon adding 1 to it, I got: 00000000000000000000000000000001
Now shifting one position right: 00000000000000000000000000000000
After flipping the bits, I got: 11111111111111111111111111111111
Now adding 1 to it: 00000000000000000000000000000000
我不明白怎么1 -1 >> -1本身，然后呢？
I don't understand how -1>>1 is -1 itself, then?
推荐答案
当你做一个正常的右移（即使用＆GT;＆GT; ，也称为的算术的右移，而不是＆GT;＆GT;＆GT; ，这是一个的逻辑的右移）时，号的符号扩展的
When you do a normal right-shift (i.e. using >>, also known as an arithmetic right shift, as opposed to >>>, which is a logical right shift), the number is sign extended.
这是如何工作如下：
当我们右移，我们得到的号码前面的空白点，像这样：
When we right-shift we get an empty spot in front of the number, like so:
11111111111111111111111111111111
?1111111111111111111111111111111(1) (right-shift it one place)
最后一个 1 被移出，并在来了？。
现在，我们该怎么填写？取决于我们如何转变。
Now, how we fill in the ? is dependent on how we shift.
如果我们做的逻辑移位的（即＆GT;＆GT;＆GT; ），我们简单地用填充0 。
如果我们做一个的算术移位的（即＆GT;＆GT; ），我们从原来的号码的第一位填充，即符号位的（因为它是 1 如果数字为负，而 0 如果不）。这就是所谓的符号扩展。
If we do a logical shift (i.e. >>>), we simply fill it with 0.
If we do a arithmetic shift (i.e. >>), we fill it with the first bit from the original number, i.e. the sign bit (since it's 1 if the number is negative, and 0 if not). This is called sign extension.
因此，在这种情况下， -1 GT;＆GT; 1 登录扩展了 1 到？，离开原来的 1 。
So, in this case, -1 >> 1 sign-extends the 1 into the ?, leaving the original -1.
- Arithmetic shift on Wikipedia
- Logical shift on Wikipedia
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