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因此,我编写了一个相当愚蠢的程序,只是为了稍微使用 nanoTime。我希望能够检查少量代码的执行时间,所以我认为 nanoTime 是最好的。我想确定这段代码的平均执行时间,所以我把它放在一个 for 循环中。然而,当在 for 循环中时,平均下降到大约 6,000 纳秒。我知道这对小代码来说并没有太大的区别,但我很好奇为什么对于相同的确切代码会有任何不同?这是产生不同时间的两个块:这个平均约为 8064 纳秒:

  long start, end, totalTime;
  double milliseconds, seconds, minutes, hours, days, years;
  totalTime = 0;

  start = System.nanoTime();
  milliseconds = System.currentTimeMillis();
  seconds = milliseconds/1000;
  minutes = seconds/60;
  hours = minutes/60;
  days = hours/24;
  years = days/365;
  end = System.nanoTime();
  totalTime = end-start;

这个平均约为 2200 纳秒:

  long start, end, totalTime;
  double milliseconds, seconds, minutes, hours, days, years;
  totalTime = 0;


  for(int i = 1; i < 11; i++){
     start = System.nanoTime();
     milliseconds = System.currentTimeMillis();
     seconds = milliseconds/1000;
     minutes = seconds/60;
     hours = minutes/60;
     days = hours/24;
     years = days/365;
     end = System.nanoTime();
     totalTime += end-start;
     System.out.println(end-start); //this was added to manually calc. the average to 
    //make sure the code was executing properly. does not effect execution time.
  }

然后找到你所用的平均值 totalTime*.1

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1 回答 1

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这正是您对任何Java 程序所期望的。Java 运行时,特别是 JIT 编译器,将在程序的整个生命周期中运行得越多,就越会优化代码。您应该期望代码在多次运行后加速。

于 2016-04-12T22:23:31.883 回答