如果您不使用工具，并且希望对执行时间较短的方法进行计时，那么只需执行多次，每次将执行次数增加一倍，直到达到1秒左右。因此，系统调用的时间。纳米时间等，也没有系统的准确性。nanoTime确实对结果有很大影响。

    int runs = 0, runsPerRound = 10;
    long begin = System.nanoTime(), end;
    do {
        for (int i=0; i<runsPerRound; ++i) timedMethod();
        end = System.nanoTime();
        runs += runsPerRound;
        runsPerRound *= 2;
    } while (runs < Integer.MAX_VALUE / 2 && 1000000000L > end - begin);
    System.out.println("Time for timedMethod() is " + 
        0.000000001 * (end-begin) / runs + " seconds");

当然，使用挂钟也有一些注意事项:jit编译、多线程/进程等的影响。因此，您需要首先执行该方法很多次，以便JIT编译器完成它的工作，然后重复此测试多次，并使用最短的执行时间。

下面是打印好的字符串，格式化后的秒数，类似于谷歌搜索所需的时间:

        long startTime = System.nanoTime();
        //  ... methodToTime();
        long endTime = System.nanoTime();
        long duration = (endTime - startTime);
        long seconds = (duration / 1000) % 60;
        // formatedSeconds = (0.xy seconds)
        String formatedSeconds = String.format("(0.%d seconds)", seconds);
        System.out.println("formatedSeconds = "+ formatedSeconds);
        // i.e actual formatedSeconds = (0.52 seconds)

JEP 230:微基准测试套件

供参考，JEP 230: Microbenchmark Suite是一个OpenJDK项目，用于:

向JDK源代码中添加一套基本的微基准测试，使开发人员可以轻松地运行现有的微基准测试和创建新的微基准测试。

这个特性是在Java 12中出现的。

Java微基准测试工具(JMH)

对于Java的早期版本，请查看JEP 230所基于的Java Microbenchmark Harness (JMH)项目。

我们也可以使用Apache公共的StopWatch类来测量时间。

示例代码

org.apache.commons.lang.time.StopWatch sw = new org.apache.commons.lang.time.StopWatch();

System.out.println("getEventFilterTreeData :: Start Time : " + sw.getTime());
sw.start();

// Method execution code

sw.stop();
System.out.println("getEventFilterTreeData :: End Time : " + sw.getTime());

在Spring框架中我们有一个叫做StopWatch的调用(org。Spring framework。util。StopWatch)

//measuring elapsed time using Spring StopWatch
        StopWatch watch = new StopWatch();
        watch.start();
        for(int i=0; i< 1000; i++){
            Object obj = new Object();
        }
        watch.stop();
        System.out.println("Total execution time to create 1000 objects in Java using StopWatch in millis: "
                + watch.getTotalTimeMillis());

在Java 8中引入了一个名为Instant的新类。根据文件:

Instant represents the start of a nanosecond on the time line. This class is useful for generating a time stamp to represent machine time. The range of an instant requires the storage of a number larger than a long. To achieve this, the class stores a long representing epoch-seconds and an int representing nanosecond-of-second, which will always be between 0 and 999,999,999. The epoch-seconds are measured from the standard Java epoch of 1970-01-01T00:00:00Z where instants after the epoch have positive values, and earlier instants have negative values. For both the epoch-second and nanosecond parts, a larger value is always later on the time-line than a smaller value.

这可以用于:

Instant start = Instant.now();
try {
    Thread.sleep(7000);
} catch (InterruptedException e) {
    e.printStackTrace();
}
Instant end = Instant.now();
System.out.println(Duration.between(start, end));

打印pt7.001。