这个布尔“（数字& 1）== 0”是什么？意思？ [英] What does this boolean "(number & 1) == 0" mean?

问题描述

在CodeReview 上我发布了一段代码，并询问了改进它的提示。我得到的是使用布尔方法来检查ArrayList是否具有偶数个索引（这是必需的）。这是建议的代码：

On CodeReview I posted a working piece of code and asked for tips to improve it. One I got was to use a boolean method to check if an ArrayList had an even number of indices (which was required). This was the code that was suggested:

private static boolean isEven(int number)
{
    return (number & 1) == 0;
}

因为我已经为那个特定用户提供了很多帮助，我我决定是时候纠缠SO社区了！我真的不明白这是如何工作的。调用该方法并将ArrayList的大小作为参数（即ArrayList有十个元素，数字= 10）。

As I've already pestered that particular user for a lot of help, I've decided it's time I pestered the SO community! I don't really understand how this works. The method is called and takes the size of the ArrayList as a parameter (i.e. ArrayList has ten elements, number = 10).

我知道一个& 运行数字和1的比较，但之后我迷路了。

I know a single & runs the comparison of both number and 1, but I got lost after that.

我读它的方式，它说的是如果 number == 0 和 1 == 0 ，则返回true。我知道第一个不是真的，后者显然没有意义。有人可以帮助我吗？

The way I read it, it is saying return true if number == 0 and 1 == 0. I know the first isn't true and the latter obviously doesn't make sense. Could anybody help me out?

编辑：我应该补充说代码确实有效，万一有人想知道。

推荐答案

请记住&是一个按位操作。您可能已经意识到这一点，但根据您提出问题的方式，我并不完全清楚。

Keep in mind that "&" is a bitwise operation. You are probably aware of this, but it's not totally clear to me based on the way you posed the question.

话虽如此，理论上的想法是你有一些int，可以用一些1和0的系列表示。例如：

That being said, the theoretical idea is that you have some int, which can be expressed in bits by some series of 1s and 0s. For example:

...10110110

在二进制中，因为它是基数2，只要数字的按位版本以0结尾，它就是偶数，当它以1结尾时它是奇数。

In binary, because it is base 2, whenever the bitwise version of the number ends in 0, it is even, and when it ends in 1 it is odd.

因此，做一个按位&上面的1是：

Therefore, doing a bitwise & with 1 for the above is:

...10110110 & ...00000001

当然，这是0，所以你可以说原始输入是均匀的。

Of course, this is 0, so you can say that the original input was even.

或者，考虑一个奇数。例如，将1添加到上面的内容中。那么

Alternatively, consider an odd number. For example, add 1 to what we had above. Then

...10110111 & ...00000001

等于1，因此不等于零。 Voila。

Is equal to 1, and is therefore, not equal to zero. Voila.

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