我发现这段代码在计时时很有用:

public class Et {
    public Et() {
    reset();
    }
    public void reset() {
    t0=System.nanoTime();
    }
    public long t0() {
        return t0;
    }
    public long dt() {
        return System.nanoTime()-t0();
    }
    public double etms() {
    return etms(dt());
    }
    @Override public String toString() {
        return etms()+" ms.";
    }
    public static double etms(long dt) {
        return dt/1000000.; // 1_000_000. breaks cobertura
    }
    private Long t0;
}

我建立了一个格式化函数，基于我偷来的东西。我需要一种方法来“分析”日志消息中的内容，所以我需要一个固定长度的持续时间消息。

public static String GetElapsed(long aInitialTime, long aEndTime, boolean aIncludeMillis)
{
  StringBuffer elapsed = new StringBuffer();

  Map<String, Long> units = new HashMap<String, Long>();

  long milliseconds = aEndTime - aInitialTime;

  long seconds = milliseconds / 1000;
  long minutes = milliseconds / (60 * 1000);
  long hours = milliseconds / (60 * 60 * 1000);
  long days = milliseconds / (24 * 60 * 60 * 1000);

  units.put("milliseconds", milliseconds);
  units.put("seconds", seconds);
  units.put("minutes", minutes);
  units.put("hours", hours);
  units.put("days", days);

  if (days > 0)
  {
    long leftoverHours = hours % 24;
    units.put("hours", leftoverHours);
  }

  if (hours > 0)
  {
    long leftoeverMinutes = minutes % 60;
    units.put("minutes", leftoeverMinutes);
  }

  if (minutes > 0)
  {
    long leftoverSeconds = seconds % 60;
    units.put("seconds", leftoverSeconds);
  }

  if (seconds > 0)
  {
    long leftoverMilliseconds = milliseconds % 1000;
    units.put("milliseconds", leftoverMilliseconds);
  }

  elapsed.append(PrependZeroIfNeeded(units.get("days")) + " days ")
      .append(PrependZeroIfNeeded(units.get("hours")) + " hours ")
      .append(PrependZeroIfNeeded(units.get("minutes")) + " minutes ")
      .append(PrependZeroIfNeeded(units.get("seconds")) + " seconds ")
      .append(PrependZeroIfNeeded(units.get("milliseconds")) + " ms");

  return elapsed.toString();

}

private static String PrependZeroIfNeeded(long aValue)
{
  return aValue < 10 ? "0" + aValue : Long.toString(aValue);
}

和一个测试类:

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

import junit.framework.TestCase;

public class TimeUtilsTest extends TestCase
{

  public void testGetElapsed()
  {
    long start = System.currentTimeMillis();
    GregorianCalendar calendar = (GregorianCalendar) Calendar.getInstance();
    calendar.setTime(new Date(start));

    calendar.add(Calendar.MILLISECOND, 610);
    calendar.add(Calendar.SECOND, 35);
    calendar.add(Calendar.MINUTE, 5);
    calendar.add(Calendar.DAY_OF_YEAR, 5);

    long end = calendar.getTimeInMillis();

    assertEquals("05 days 00 hours 05 minutes 35 seconds 610 ms", TimeUtils.GetElapsed(start, end, true));

  }

}

值得注意的是

System.currentTimeMillis() has only millisecond accuracy at best. At worth its can be 16 ms on some windows systems. It has a lower cost that alternatives < 200 ns. System.nanoTime() is only micro-second accurate on most systems and can jump on windows systems by 100 microseconds (i.e sometimes it not as accurate as it appears) Calendar is a very expensive way to calculate time. (i can think of apart from XMLGregorianCalendar) Sometimes its the most appropriate solution but be aware you should only time long intervals.

Byte Stream Reader Elapsed Time for 23.7 MB is 96 secs

import java.io.*;
import java.io.IOException;
import java.util.Scanner;

class ElaspedTimetoCopyAFileUsingByteStream
{

    private long startTime = 0;
    private long stopTime = 0;
    private boolean running = false;


    public void start() 
    {
        this.startTime = System.currentTimeMillis();
        this.running = true;
    }


    public void stop() 
    {
        this.stopTime = System.currentTimeMillis();
        this.running = false;
    }



    public long getElapsedTime() 
    {
        long elapsed;
        if (running) {
             elapsed = (System.currentTimeMillis() - startTime);
        }
        else {
            elapsed = (stopTime - startTime);
        }
        return elapsed;
    }



    public long getElapsedTimeSecs()                 
    {
        long elapsed;
        if (running) 
        {
            elapsed = ((System.currentTimeMillis() - startTime) / 1000);
        }
        else
        {
            elapsed = ((stopTime - startTime) / 1000);
        }
        return elapsed;
    }





    public static void main(String[] args) throws IOException
    {
        ElaspedTimetoCopyAFileUsingByteStream  s = new ElaspedTimetoCopyAFileUsingByteStream();
        s.start();

        FileInputStream in = null;
        FileOutputStream out = null;

      try {
         in = new FileInputStream("vowels.txt");   // 23.7  MB File
         out = new FileOutputStream("output.txt");

         int c;
         while ((c = in.read()) != -1) {
            out.write(c);
         }
      }finally {
         if (in != null) {
            in.close();
         }
         if (out != null) {
            out.close();
         }
      }



        s.stop();
        System.out.println("elapsed time in seconds: " + s.getElapsedTimeSecs());
    }
}

[Elapsed Time for Byte Stream Reader][1]

**Character Stream Reader Elapsed Time for 23.7 MB is 3 secs**

import java.io.*;
import java.io.IOException;
import java.util.Scanner;

class ElaspedTimetoCopyAFileUsingCharacterStream
{

    private long startTime = 0;
    private long stopTime = 0;
    private boolean running = false;


    public void start() 
    {
        this.startTime = System.currentTimeMillis();
        this.running = true;
    }


    public void stop() 
    {
        this.stopTime = System.currentTimeMillis();
        this.running = false;
    }



    public long getElapsedTime() 
    {
        long elapsed;
        if (running) {
             elapsed = (System.currentTimeMillis() - startTime);
        }
        else {
            elapsed = (stopTime - startTime);
        }
        return elapsed;
    }



    public long getElapsedTimeSecs()                 
    {
        long elapsed;
        if (running) 
        {
            elapsed = ((System.currentTimeMillis() - startTime) / 1000);
        }
        else
        {
            elapsed = ((stopTime - startTime) / 1000);
        }
        return elapsed;
    }





    public static void main(String[] args) throws IOException
    {
        ElaspedTimetoCopyAFileUsingCharacterStream  s = new ElaspedTimetoCopyAFileUsingCharacterStream();
        s.start();

         FileReader in = null;                // CharacterStream Reader
      FileWriter out = null;

      try {
         in = new FileReader("vowels.txt");    // 23.7 MB
         out = new FileWriter("output.txt");

         int c;
         while ((c = in.read()) != -1) {
            out.write(c);
         }
      }finally {
         if (in != null) {
            in.close();
         }
         if (out != null) {
            out.close();
         }
      }

              s.stop();
        System.out.println("elapsed time in seconds: " + s.getElapsedTimeSecs());
    }
}


[Elapsed Time for Character Stream Reader][2]


  [1]: https://i.stack.imgur.com/hYo8y.png
  [2]: https://i.stack.imgur.com/xPjCK.png

如果您从System.currentTimeMillis()获取时间戳，那么您的时间变量应该是长变量。

如果您正在编写一个必须处理持续时间的应用程序，那么请查看Joda-Time，它有专门处理持续时间、间隔和周期的类。你的getDuration()方法看起来可以返回一个Joda-Time Interval:

DateTime start = new DateTime(2004, 12, 25, 0, 0, 0, 0);
DateTime end = new DateTime(2005, 1, 1, 0, 0, 0, 0);

public Interval getInterval() {
    Interval interval = new Interval(start, end);
}