在Java中，获取系统时间最快的方法是什么？

Question

我正在开发一个经常使用系统时间的系统，因为Delayed接口。

从系统获取时间的最快方法是什么？

目前我每次需要获取时间时都使用Calendar.getInstance().getTimeInMillis() ，但我不知道是否有更快的方法。

Answer 1

System.currentTimeMillis()
“以毫秒为单位返回当前时间” 。
使用它来获取实际的系统时间。

System.nanoTime() 。
“返回的值表示自某个固定但任意的原始时间以来的纳秒”
使用它是您正在测量时间流逝/事件。

Answer 2

对于较大的请求数，我认为应该有一个线程负责更新当前系统时间，避免每个线程独立执行。

Answer 3

简而言之， System.currentTimeMillis()更快。

@Test
public void testSystemCurrentTime() {
    final Stopwatch stopwatch = Stopwatch.createStarted();
    for (int i = 0; i < 1_00_000; i++) {
        System.currentTimeMillis();
    }
    stopwatch.stop();
    System.out.println("System.currentTimeMillis(): " + stopwatch);
}

@Test
public void testDateTime() {
    final Stopwatch stopwatch = Stopwatch.createStarted();
    for (int i = 0; i < 1_00_000; i++) {
        (new Date()).getTime();
    }
    stopwatch.stop();
    System.out.println("(new Date()).getTime(): " + stopwatch);
}

@Test
public void testCalendarTime() {
    final Stopwatch stopwatch = Stopwatch.createStarted();
    for (int i = 0; i < 1_00_000; i++) {
        Calendar.getInstance().getTimeInMillis();
    }
    stopwatch.stop();
    System.out.println("Calendar.getInstance().getTimeInMillis(): " + stopwatch);
}

我跑了上面的测试用例，我发现了以下结果：

System.currentTimeMillis(): 5.208 ms    (new Date()).getTime(): 19.57 ms    Calendar.getInstance().getTimeInMillis(): 148.2 ms
System.currentTimeMillis(): 4.685 ms    (new Date()).getTime(): 11.53 ms    Calendar.getInstance().getTimeInMillis(): 122.6 ms
System.currentTimeMillis(): 4.734 ms    (new Date()).getTime(): 11.66 ms    Calendar.getInstance().getTimeInMillis(): 131.5 ms
System.currentTimeMillis(): 4.018 ms    (new Date()).getTime(): 19.33 ms    Calendar.getInstance().getTimeInMillis(): 127.6 ms
System.currentTimeMillis(): 5.474 ms    (new Date()).getTime(): 16.74 ms    Calendar.getInstance().getTimeInMillis(): 113.6 ms
System.currentTimeMillis(): 3.871 ms    (new Date()).getTime(): 14.46 ms    Calendar.getInstance().getTimeInMillis(): 120.5 ms
System.currentTimeMillis(): 8.223 ms    (new Date()).getTime(): 11.65 ms    Calendar.getInstance().getTimeInMillis(): 173.8 ms
System.currentTimeMillis(): 4.611 ms    (new Date()).getTime(): 9.978 ms    Calendar.getInstance().getTimeInMillis(): 117.9 ms
System.currentTimeMillis(): 3.794 ms    (new Date()).getTime(): 11.33 ms    Calendar.getInstance().getTimeInMillis(): 89.79 ms
System.currentTimeMillis(): 4.298 ms    (new Date()).getTime(): 12.37 ms    Calendar.getInstance().getTimeInMillis(): 123.8 ms

我希望这能帮到您。

Answer 4

System.currentTimeMillis()根据以下测试用例最快

public class ClassTest
{
    @Test
    public void testSystemCurrentTime()
    {
        final Stopwatch stopwatch = Stopwatch.createStarted();
        for (int i = 0; i < 1_00_000; i++)
        {
            System.currentTimeMillis();
        }
        stopwatch.stop();
        System.out.println("System.currentTimeMillis(): " + stopwatch);
    }

    @Test
    public void testDateTime()
    {
        final Stopwatch stopwatch = Stopwatch.createStarted();
        for (int i = 0; i < 1_00_000; i++)
        {
            (new Date()).getTime();
        }
        stopwatch.stop();
        System.out.println("(new Date()).getTime(): " + stopwatch);
    }

    @Test
    public void testCalendarTime()
    {
        final Stopwatch stopwatch = Stopwatch.createStarted();
        for (int i = 0; i < 1_00_000; i++)
        {
            Calendar.getInstance().getTimeInMillis();
        }
        stopwatch.stop();
        System.out.println("Calendar.getInstance().getTimeInMillis(): " + stopwatch);
    }

    @Test
    public void testInstantNow()
    {
        final Stopwatch stopwatch = Stopwatch.createStarted();
        for (int i = 0; i < 1_00_000; i++)
        {
            Instant.now();
        }
        stopwatch.stop();
        System.out.println("Instant.now(): " + stopwatch);
    }
}

Output：

(new Date()).getTime(): 36.89 ms
Calendar.getInstance().getTimeInMillis(): 448.0 ms
Instant.now(): 34.13 ms
System.currentTimeMillis(): 10.28 ms

但是，

Instant.now()更快+更简单，并提供其他实用程序以及Instant.now().getEpochSecond(); , Instant.now().getNano(); , Instant.now().compareTo(otherInstant); 还有很多。

Answer 5

long timeMilliSec = System.currentTimeMillis();

Answer 6

System.currentTimeMillis()可能。

Answer 7

System.currentTimeMillis 

是简单的答案