如何使用 System.currentTimeMillis() 以秒为单位测量时间跨度？

Question

如何转换System.currentTimeMillis(); 到秒？

long start6=System.currentTimeMillis();
System.out.println(counter.countPrimes(100000000)+" for "+start6);

控制台向我显示5761455 for 1307816001290 。 我看不懂那是多少秒。

有什么帮助吗？

Answer 1

TimeUnit

使用 Java 5 及更高版本中内置的TimeUnit 枚举。

long timeMillis = System.currentTimeMillis();
long timeSeconds = TimeUnit.MILLISECONDS.toSeconds(timeMillis);

Answer 2

long start = System.currentTimeMillis();
counter.countPrimes(1000000);
long end = System.currentTimeMillis();

System.out.println("Took : " + ((end - start) / 1000));

更新

更准确的解决方案是：

final long start = System.nanoTime();
counter.countPrimes(1000000);
final long end = System.nanoTime();

System.out.println("Took: " + ((end - start) / 1000000) + "ms");
System.out.println("Took: " + (end - start)/ 1000000000 + " seconds");

Answer 3

像这样：

(int)(milliseconds / 1000)

Answer 4

Java 8 现在提供了获取当前 Unix 时间戳的最简洁方法：

Instant.now().getEpochSecond();

Answer 5

从您的代码看来，您正在尝试测量计算花费了多长时间（而不是试图弄清楚当前时间是多少）。

在这种情况下，您需要在计算之前和之后调用currentTimeMillis ，取其差，然后将结果除以 1000 以将毫秒转换为秒。

Answer 6

我在上次作业中编写了以下代码，它可能会对您有所帮助：

// A method that converts the nano-seconds to Seconds-Minutes-Hours form
private static String formatTime(long nanoSeconds)
{
    int hours, minutes, remainder, totalSecondsNoFraction;
    double totalSeconds, seconds;


    // Calculating hours, minutes and 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;
    if(arr[1].contains("E")) seconds = Double.parseDouble("." + arr[1]);
    else seconds += Double.parseDouble("." + arr[1]);


    // Formatting the string that conatins hours, minutes and seconds
    StringBuilder result = new StringBuilder(".");
    String sep = "", nextSep = " and ";
    if(seconds > 0)
    {
        result.insert(0, " seconds").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();
}

只需将纳秒转换为毫秒。

Answer 7

TimeUnit.SECONDS.convert(start6, TimeUnit.MILLISECONDS);

Answer 8

对于毫秒到秒的转换，因为 1 秒 = 10³ 毫秒：

//here m will be in seconds
long m = System.currentTimeMillis()/1000;

//here m will be in minutes
long m = System.currentTimeMillis()/1000/60; //this will give in mins

Answer 9

// Convert millis to seconds. This can be simplified a bit,
// but I left it in this form for clarity.
long m = System.currentTimeMillis(); // that's our input
int s = Math.max(
  .18 * (Math.toRadians(m)/Math.PI),
  Math.pow( Math.E, Math.log(m)-Math.log(1000) )
);
System.out.println( "seconds: "+s );