所以,我試圖測量一些排序方法的執行時間。我的代碼測量執行時間的問題
這裏是我的代碼:
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();
}
我的問題是:
運行後這個節目,我進入int[1000000]
作爲輸入,它在約12-13分鐘內執行insertionSort()
,然後返回:
insertionSort() takes 767186856920 nano-seconds which is 12 minutes and 470.18685692 seconds.
爲什麼它給470秒?我的代碼有什麼問題?
=========================
編輯:
與seconds = seconds + Double.parseDouble("." + arr[1]);
,上期更換seconds = Double.parseDouble(Long.toString((long)seconds) + Double.parseDouble("." + arr[1]));
後是走了,但另一個問題出現了:
insertionSort() takes 22864 nano-seconds which is 2.000002864 seconds.
應該0.000022864 seconds.
=========================
EDIT2:
我可能發現了錯誤。當nanoSeconds
很大時,arr[1]
將會正常,但當nanoSeconds
較小時,arr[1]
將轉換爲指數形式,即14931 nano-seconds => 4.931E-6 seconds.
。我該如何解決這個問題?
==========================
EDIT3:
好吧,我找到了解決辦法:
if(arr[1].contains("E")) seconds = Double.parseDouble("." + arr[1]);
else seconds += Double.parseDouble("." + arr[1]);
對不起,另一個問題出現了,我不得不取消選擇這個答案 – 2011-05-20 02:56:16