Java中的时间精度

    在Java中可以通过System.currentTimeMillis()或者System.nanoTime() (JDK>=5.0) 方法获得当前的时间的精确值。但是通过阅读Javadoc，我们发现这两个方法并不一定保证得到你所期望的精度。先来看System.currentTimeMillis()：
Returns the current time in milliseconds. Note that while the unit of time of
the return value is a millisecond, the granularity of the value depends on the
underlying operating system and may be larger. For example, many operating
systems measure time in units of tens of milliseconds.
诚如上面所说返回值的粒度依赖于底层操作系统，那么它在不同的平台上到底能提供是么样的精度，是否像函数名所写的那样真正
精
确到1毫秒呢？看下面一段测试程序：
public class ClockAccuracyTest {
    public static void main(String args[]) {
        SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss:SSS");
        int size = 4000000;
        // create an array to hold millisecond times
        // and loop to capture them
        long times[] = new long[size];
        for (int i = 0; i < size; i++) {
            times[i] = System.currentTimeMillis();
        }
        // now display the unique times
        long time = times[0];
        long previousTime = times[0];
        long count = 0;
        Set<Long> deltas = new HashSet<Long>();       
        long delta = 0;
        long minDelta = Long.MAX_VALUE;
        long maxDelta = Long.MIN_VALUE;
    &