奇怪吗?

(value & 0x1) > 0

它能被2(偶数)整除吗?

(value & 0x1) == 0

还没人提到过收藏。有时您有一个较小的可能值集合，比如只有10或20个可能值，您希望将其中一些值保存在一个集合中。当然，您可以使用常规的Set实现，它很可能使用支持哈希表。但由于可能值的集合是如此之小，这实际上只是浪费时间和空间。相反，您可以将集合存储在单个int或长值中，这正是java EnumSet所做的，如果我没记错的话。

我见过它们在基于角色的访问控制系统中使用。

Bit fields (flags) They're the most efficient way of representing something whose state is defined by several "yes or no" properties. ACLs are a good example; if you have let's say 4 discrete permissions (read, write, execute, change policy), it's better to store this in 1 byte rather than waste 4. These can be mapped to enumeration types in many languages for added convenience. Communication over ports/sockets Always involves checksums, parity, stop bits, flow control algorithms, and so on, which usually depend on the logic values of individual bytes as opposed to numeric values, since the medium may only be capable of transmitting one bit at a time. Compression, Encryption Both of these are heavily dependent on bitwise algorithms. Look at the deflate algorithm for an example - everything is in bits, not bytes. Finite State Machines I'm speaking primarily of the kind embedded in some piece of hardware, although they can be found in software too. These are combinatorial in nature - they might literally be getting "compiled" down to a bunch of logic gates, so they have to be expressed as AND, OR, NOT, etc. Graphics There's hardly enough space here to get into every area where these operators are used in graphics programming. XOR (or ^) is particularly interesting here because applying the same input a second time will undo the first. Older GUIs used to rely on this for selection highlighting and other overlays, in order to eliminate the need for costly redraws. They're still useful in slow graphics protocols (i.e. remote desktop).

这些只是我最先想到的几个例子——这不是一个详尽的清单。

我的问题在现实世界中是有用的 只响应第一个WM_KEYDOWN通知?

当在windows C api中使用WM_KEYDOWN消息时，第30位指定前一个键的状态。如果在发送消息之前键为down，则值为1;如果键为up，则值为0

奇怪吗?

(value & 0x1) > 0

它能被2(偶数)整除吗?

(value & 0x1) == 0