Efficiency comparison of three methods for obtaining timestamp

1.System.currentTimeMillis()

System Class currentTimeMillis() The method is the most efficient of the three , The shortest running time . In the development, if the design comes to the problem of efficiency , It is recommended to use this method to obtain .

2.new Date().getTime()

except System class , The ones that use a lot should be Date The class , but date Getting a timestamp in a class is not the most efficient , Look at his source code :
The parameterless structure is as follows
public Date() {
this(System.currentTimeMillis());
}
You can see from the source code ,new Date() It's actually called System.currentTimeMillis(), Then pass in your own parameter constructor .
It's not hard to see. , If you just get the timestamp , Even anonymous new Date() Objects also have a slight performance cost , From the perspective of improving performance , Just get the timestamp , Regardless of the time zone ,
Call directly System.currentTimeMillis() It will be better .

3.Calendar.getInstance().getTimeInMillis()

This method is actually the slowest , Look at its source code and you will find ,Canlendar It's time zone sensitive , Because it takes a lot of time to deal with the time zone problem .

package com.example.java_algorithms.javaBasic.time;

import java.util.Calendar;
import java.util.Date;

/** *  Efficiency comparison of three time stamp acquisition methods  */
public class TimeStampComparable {
    
        private static long _TEN_THOUSAND=10000;
        public static void main(String[] args) {
    
            long times=1000*_TEN_THOUSAND;
            long t1=System.currentTimeMillis();
            testSystem(times);
            long t2=System.currentTimeMillis();
            System.out.println(t2-t1);

            testCalander(times);
            long t3=System.currentTimeMillis();
            System.out.println(t3-t2);

            testDate(times);
            long t4=System.currentTimeMillis();
            System.out.println(t4-t3);
            /** testSystem:28 testCalander:1513 testDate:29 */
        }

        public static void testSystem(long times){
    //use 188
            for(int i=0;i<times;i++){
    
                long currentTime=System.currentTimeMillis();
            }
        }

        public static void testCalander(long times){
    //use 6299
            for(int i=0;i<times;i++){
    
                long currentTime= Calendar.getInstance().getTimeInMillis();
            }
        }

        public static void testDate(long times){
    
            for(int i=0;i<times;i++){
    
                long currentTime=new Date().getTime();
            }
        }
    }