(1) Include a Data class in the standard Java class library. Its object represents a specific instant, accurate to the millisecond
(2) The representation of time in Java is also a number, which is the number of milliseconds from 0:00 on January 1, 1970 of the standard era to a certain moment, the type is long
import java.util.Date;
Date d = new Date(); //No-argument constructor, representing the current moment
System,out.println(d); //Print time
System.out.println(d.getTime()); //Get the long value of time
Date d2 = new Date(3600); //Constructor with parameters, the unit is milliseconds
System,out.println(d2.toGMTString()); //The printing time is 1:00 on January 1, 1990. If .toGMTString() is not added, it will print 9:00 Beijing time
d2.setTime(1000); //Reset the time