Calendario getTimeInMillis() Método en Java con ejemplos

El método getTimeInMillis() en la clase Calendario se usa para devolver la hora actual de este Calendario en milisegundos.
Sintaxis: 
 

public long getTimeInMillis()

Parámetros: El método no toma ningún parámetro.
Valor devuelto: el método devuelve la hora actual de este calendario en milisegundos.
Los siguientes programas ilustran el funcionamiento del método getTimeInMillis() de la clase Calendario: 
Ejemplo 1:
 

// Java code to illustrate
// getTimeInMillis() method
 
import java.util.*;
 
public class Calendar_Demo {
 
    public static void main(String args[])
        throws InterruptedException
    {
 
        // Creating a calendar
        Calendar calndr1 = Calendar.getInstance();
 
        // Displaying the current time
        System.out.println("The Current Time"
                           + " is: "
                           + calndr1.getTimeInMillis());
 
        // Adding few delay
        Thread.sleep(10000);
 
        // Creating another calendar
        Calendar calndr2 = Calendar.getInstance();
 
        // Displaying the upcoming time
        System.out.println("The Upcoming Time"
                           + " is: "
                           + calndr2.getTimeInMillis());
    }
}

The Current Time is: 1550725664034
The Upcoming Time is: 1550725674053

Ejemplo 2: 
 

// Java code to illustrate
// getTimeInMillis() method
 
import java.util.*;
 
public class Calendar_Demo {
 
    public static void main(String args[])
        throws InterruptedException
    {
 
        // Creating a calendar
        Calendar calndr1 = Calendar.getInstance();
 
        // Displaying the current time
        System.out.println("The Current Time"
                           + " is: "
                           + calndr1.getTimeInMillis());
 
        // Adding few delay
        Thread.sleep(5000);
 
        // Creating another calendar
        Calendar calndr2 = Calendar.getInstance();
 
        // Displaying the upcoming time
        System.out.println("The Upcoming Time"
                           + " is: "
                           + calndr2.getTimeInMillis());
    }
}

The Current Time is: 1550725683182
The Upcoming Time is: 1550725688208

Referencia: https://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html#getTimeInMillis–