Java: How to increment only the time in a date?

package com.peterleow;

import java.util.Calendar;

public class exercise1 {

    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance();

        System.out.println(calendar.getTime());

        calendar.add(Calendar.HOUR,  1);

        System.out.println(calendar.getTime());

    }

}