System.currentTimeMillis()与GMT

一、System.currentTimeMillis()函数注释

public final class System {
   /**
     * 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.
     *
     * <p> See the description of the class <code>Date</code> for
     * a discussion of slight discrepancies that may arise between
     * "computer time" and coordinated universal time (UTC).
     *
     * @return  the difference, measured in milliseconds, between
     *          the current time and midnight, January 1, 1970 UTC.
     * @see     java.util.Date
     */
    public static native long currentTimeMillis();
}

二、说明

System.currentTimeMillis()函数获取的是格林威治（GMT）自1970-1-1起始的毫秒数，也称为epoch。

例如：我在东八区的2020-11-24 13:00调用该函数获取的毫秒数为1606194000；
而该毫秒数相对于1970-1-1的时间为2020-11-24 5:00，即GMT时间；

三、结论

1. 在时间准确的前提下，某一时刻在全球各个时区调用System.currentTimeMillis()的结果是一样的。