How Java calculates program run time

Long startTime = System.currenttimemillis (); Get Start time

DoSomething (); Code snippet for testing

Long endTime = System.currenttimemillis (); Get End time

SYSTEM.OUT.PRINTLN ("program Run Time:" + (Endtime-starttime) + "MS"); Output program run time

The second is measured in nanoseconds.

Long Starttime=system.nanotime (); Get Start time

DoSomething (); Code snippet for testing

Long Endtime=system.nanotime (); Get End time

SYSTEM.OUT.PRINTLN ("program Run Time:" + (Endtime-starttime) + "ns");

public static void Main (String[]args) {
  String str= "";
  Long Startime=system.currenttimemillis ();
  Calculate the time of loop 10000
  for (int i=0;i<10000;i++) {
   Str=str+i;
  }
  Long Endtime=system.currenttimemillis ();
  Long Time=endtime-startime;
  System.out.println (time);
  StringBuilder bulider=new StringBuilder ("");
  Startime=system.currenttimemillis ();
  for (int j=0;j<10000;j++) {
   Bulider.append (j);
  }
  Endtime=system.currenttimemillis ();
  Time=endtime-startime;
  System.out.println (time);
}

How Java calculates program run time