How to calculate time difference in java?

Java 8 has a cleaner solution - Instant and Duration

Example:

import java.time.Duration;
import java.time.Instant;
...
Instant start = Instant.now();
//your code
Instant end = Instant.now();
Duration timeElapsed = Duration.between(start, end);
System.out.println("Time taken: "+ timeElapsed.toMillis() +" milliseconds");

String time1 = "16:00:00";
String time2 = "19:00:00";

SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss");
Date date1 = format.parse(time1);
Date date2 = format.parse(time2);
long difference = date2.getTime() - date1.getTime(); 

Difference is in milliseconds.

I modified sfaizs post.

TO get pretty timing differences, then

// d1, d2 are dates
long diff = d2.getTime() - d1.getTime();

long diffSeconds = diff / 1000 % 60;
long diffMinutes = diff / (60 * 1000) % 60;
long diffHours = diff / (60 * 60 * 1000) % 24;
long diffDays = diff / (24 * 60 * 60 * 1000);

System.out.print(diffDays + " days, ");
System.out.print(diffHours + " hours, ");
System.out.print(diffMinutes + " minutes, ");
System.out.print(diffSeconds + " seconds.");