Use GregorianCalendar class

Calendar and GregorianCalendar is a parent-child relationship, Calendar is the parent class.

Calendar Calendar class

GregorianCalendar class usage to date such as the date of addition and subtraction

public class GregorianCalendarTest {
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        GregorianCalendar cal = new GregorianCalendar();
        Date date = new Date();
        System.out.println(sdf.format(date));
        cal.setTime(date);
        cal.add(1, 1);
        Date time = cal.getTime();
        System.out.println(sdf.format(time));
    }
}

2019-12-06
2020-12-06

public final static int YEAR = 1;
public final static int MONTH = 2;
public final static int WEEK_OF_YEAR = 3;
public final static int WEEK_OF_MONTH = 4;
public final static int DATE = 5;
public final static int DAY_OF_MONTH = 5;
public final static int DAY_OF_YEAR = 6;
public final static int DAY_OF_WEEK = 7;
public final static int DAY_OF_WEEK_IN_MONTH = 8;
public final static int AM_PM = 9;
public final static int HOUR = 10;
public final static int HOUR_OF_DAY = 11;
public final static int MINUTE = 12;
public final static int SECOND = 13;
public final static int MILLISECOND = 14;
public final static int ZONE_OFFSET = 15;
。。。。。
Calendar