如何测量 Java 中经过的时间? [英] How do I measure time elapsed in Java?

问题描述

我想要这样的东西:

public class Stream
{
    public startTime;
    public endTime;

    public getDuration()
    {
        return startTime - endTime;
    }
}

同样重要的是，例如，如果 startTime 是 23:00，endTime 是 1:00，则持续时间为 2:00.

Also it is important that for example if the startTime it's 23:00 and endTime 1:00 to get a duration of 2:00.

在 Java 中使用哪些类型来实现这一点?

Which types to use in order to accomplish this in Java?

推荐答案

不幸的是，到目前为止发布的十个答案中没有一个是完全正确的.

Unfortunately, none of the ten answers posted so far are quite right.

如果您正在测量经过的时间，并且希望它正确，则必须使用 System.nanoTime().你不能使用 System.currentTimeMillis()，除非你不介意你的结果是错误的.

If you are measuring elapsed time, and you want it to be correct, you must use System.nanoTime(). You cannot use System.currentTimeMillis(), unless you don't mind your result being wrong.

nanoTime的目的是测量elapsed时间，currentTimeMillis的目的是测量wall-clock 时间.您不能将其用于其他目的.原因是没有计算机的时钟是完美的；它总是漂移，偶尔需要纠正.这种更正可能是手动发生的，或者在大多数机器的情况下，有一个进程会运行并不断向系统时钟(挂钟")发出小的更正.这些往往经常发生.每当有闰秒时，就会发生另一个这样的修正.

The purpose of nanoTime is to measure elapsed time, and the purpose of currentTimeMillis is to measure wall-clock time. You can't use the one for the other purpose. The reason is that no computer's clock is perfect; it always drifts and occasionally needs to be corrected. This correction might either happen manually, or in the case of most machines, there's a process that runs and continually issues small corrections to the system clock ("wall clock"). These tend to happen often. Another such correction happens whenever there is a leap second.

由于 nanoTime 的目的是测量经过的时间，因此它不受任何这些小修正的影响.这是你想要使用的.currentTimeMillis 当前正在进行的任何计时都将关闭 - 甚至可能为负.

Since nanoTime's purpose is to measure elapsed time, it is unaffected by any of these small corrections. It is what you want to use. Any timings currently underway with currentTimeMillis will be off -- possibly even negative.

您可能会说，这听起来并没有那么重要"，对此我说，也许不是，但总的来说，正确的代码不是比错误的代码更好吗?此外，nanoTime 无论如何输入都更短.

You may say, "this doesn't sound like it would ever really matter that much," to which I say, maybe not, but overall, isn't correct code just better than incorrect code? Besides, nanoTime is shorter to type anyway.

之前发布的关于 nanoTime 通常只有微秒精度的免责声明是有效的.此外，根据情况(与其他情况一样)，调用可能需要一整微秒以上的时间，因此不要期望正确地计时非常非常小的时间间隔.

Previously posted disclaimers about nanoTime usually having only microsecond precision are valid. Also it can take more than a whole microsecond to invoke, depending on circumstances (as can the other one), so don't expect to time very very small intervals correctly.

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