java - 我的测量执行时间的代码存在问题

Question

所以，我正在尝试测量一些排序方法的执行时间。

这是我的代码:

public static void main(String[] args)
{
    ...

    MeasureExecutionTime(new Runnable() { public void run() { insertionSort(C); } }, "insertionSort()");
}

======================

private static void MeasureExecutionTime(Runnable r, String s)
{
    startTime = System.nanoTime();
    try
    {
        r.run();
    }
    finally
    {
        endTime = System.nanoTime();
    }
    elapsedTime = endTime - startTime;
    System.out.println(s + " takes " + elapsedTime + " nano-seconds which is " + formatTime(elapsedTime));
}

======================

public static String formatTime(long nanoSeconds)
{
    long hours, minutes, remainder, totalSecondsNoFraction;
    double totalSeconds, seconds;

    totalSeconds = (double) nanoSeconds / 1000000000.0;
    String s = Double.toString(totalSeconds);
    String [] arr = s.split("\\.");
    totalSecondsNoFraction = Integer.parseInt(arr[0]);
    hours = totalSecondsNoFraction / 3600;
    remainder = totalSecondsNoFraction % 3600;
    minutes = remainder / 60;
    seconds = remainder % 60;
    seconds = Double.parseDouble(Long.toString((long)seconds) + Double.parseDouble("." + arr[1]));

    StringBuilder result = new StringBuilder(".");
    String sep = "", nextSep = " and ";
    if(seconds > 0)
    {
        if(seconds > 1) result.insert(0, " seconds").insert(0, seconds);
        else result.insert(0, " second").insert(0, seconds);
        sep = nextSep;
        nextSep = ", ";
    }
    if(minutes > 0)
    {
        if(minutes > 1) result.insert(0, sep).insert(0, " minutes").insert(0, minutes);
        else result.insert(0, sep).insert(0, " minute").insert(0, minutes);
        sep = nextSep;
        nextSep = ", ";
    }
    if(hours > 0)
    {
        if(hours > 1) result.insert(0, sep).insert(0, " hours").insert(0, hours);
        else result.insert(0, sep).insert(0, " hour").insert(0, hours);
    }
    return result.toString();
}

我的问题是:

运行此程序后，我输入 int[1000000] 作为输入，它会在大约 12-13 分钟内执行 insertionSort()，然后返回:

insertionSort() takes 767186856920 nano-seconds which is 12 minutes and 470.18685692 seconds.

为什么给出 470 秒？我的代码出了什么问题？

==========================

编辑:

将 Seconds = Double.parseDouble(Long.toString((long)Seconds) + Double.parseDouble("."+ arr[1])); 替换为 Seconds = Seconds 后+ Double.parseDouble("."+ arr[1]);，上一个问题消失了，但又出现了一个问题:

insertionSort() takes 22864 nano-seconds which is 2.000002864 seconds.

应该是0.000022864秒。

==========================

编辑2:

我可能会发现这个错误。当nanoSeconds很大时，arr[1]就可以了，但是当nanoSeconds很小时，arr[1]将转换为指数形式，即 14931 纳秒 => 4.931E-6 秒。。我该如何解决这个问题？

============================

编辑3:

好的，我找到了解决方案:

if(arr[1].contains("E")) seconds = Double.parseDouble("." + arr[1]);
else seconds += Double.parseDouble("." + arr[1]);

Answer 1

问题出在这里:

seconds = Double.parseDouble(Long.toString((long)seconds) + 
                             Double.parseDouble("0." + arr[1]));

假设输入此行的秒为12，而arr[1]为“456”。然后

seconds = Double.parseDouble("12" + Double.parseDouble("0.456"));
seconds = Double.parseDouble("12" + 0.456);
seconds = Double.parseDouble("12" + "0.456");
seconds = Double.parseDouble("120.456");
seconds = 120.456.

为什么不这样做:

seconds = seconds + Double.parseDouble("0." + arr[1]);