Program

package IncludeHelp;

import java.util.Calendar;

public class ExAddHrsToCurrentDate {
  public static void main(String[] args) {
    // create object of calendar class.
    Calendar now = Calendar.getInstance();

    // fetch the Current date and time of the system.
    System.out.println("Current Date : " + (now.get(Calendar.MONTH) + 1) +
      "-" + now.get(Calendar.DATE) + "-" + now.get(Calendar.YEAR));
    System.out.println("Current time : " + now.get(Calendar.HOUR_OF_DAY) +
      ":" + now.get(Calendar.MINUTE) + ":" + now.get(Calendar.SECOND));

    // take default hours.
    now.add(Calendar.HOUR, 15);

    //printng date after adding 15 hours in time
    System.out.println("New Date : " + (now.get(Calendar.MONTH) + 1) + "-" +
      now.get(Calendar.DATE) + "-" + now.get(Calendar.YEAR));
    // This will show new time and date after adding hours.
    System.out.println("New time after adding 15 hours : " + now.get(Calendar.HOUR_OF_DAY) + ":" + now.get(Calendar.MINUTE) + ":" + now.get(Calendar.SECOND));
  }
}

Output

Current Date : 12-23-2017
Current time : 20:36:24
New Date : 12-24-2017
New time after adding 15 hours : 11:36:24