java example of operation

1, the date of the subtraction operation

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateCalculate {

    private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    /**
     * 获取形如yyyy-MM-dd HH:mm:ss
     * @param date
     * @return
     */
    public static String datetimeToString(Date date) {
        return sdf.format(date);
    }

    /**
     * 根据时间字符串获取日期
     * @param dateString
     * @return
     * @throws ParseException
     */
    public static Date stringToDatetime(String dateString) throws ParseException {
        return sdf.parse(dateString);
    }

    /**
     * 获取本月最后一天
     * @return
     */
    public static Date getMonthStartDate(Date date) {
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DAY_OF_MONTH,1);
        return calendar.getTime();
    }

    /**
     * 获取本月最后一天
     * @return
     */
    public static Date getMonthEndDate(Date date) {
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set (Calendar.DAY_OF_MONTH, calendar.getActualMaximum (Calendar.DAY_OF_MONTH)); 
        return calendar.getTime();
    } 


    / ** 
     * Retrieves the designated date belongs weeks start time 
     * @param DATE 
     * @return 
     * / 
    public static getBeginWeekDate a Date (a Date DATE) { 
        Calendar = Calendar.getInstance CAL (); 
        cal.setTime (DATE); 
        int = dayOfWeek cal.get (the Calendar.DAY_OF_WEEK); 
        IF (== dayOfWeek. 1) { 
            dayOfWeek + =. 7; 
        } 
        cal.add (Calendar.DATE, 2 - dayOfWeek); 
        return cal.getTime (); 
    } 

    / ** 
     * from the specified date relevant to the circumferential end time 
     * @return 
     * / 
    public static getEndWeekDate a date (a date dATE) { 
        Calendar Calendar.getInstance CAL = ();
        cal.setTime (DATE); 
        int = dayOfWeek cal.get (the Calendar.DAY_OF_WEEK); 
        IF (== dayOfWeek. 1) { 
            dayOfWeek + =. 7; 
        } 
        cal.add (Calendar.DATE,. 8 - dayOfWeek); 
        return cal.getTime (); 
    } 

    / ** 
     * year dates specified subtraction operation 
     * @param dATE 
     * @param NUM 
     * @return 
     * / 
    public static calculateDateOfYear a date (dATE a date, Integer NUM) { 
        Calendar Calendar Calendar.getInstance = (); 
        calendar.setTime (dATE); 
        Calendar.add (Calendar.YEAR, NUM); 
        return calendar.getTime();
    } 

    / ** 
     * day of the month for the specified subtraction operation 
     * @param date 
     * @param NUM 
     * @return 
     * / 
    public static calculateDateOfMonth a Date (DATE a Date, Integer NUM) { 
        Calendar Calendar Calendar.getInstance = (); 
        calendar.setTime (DATE); 
        Calendar.add (the Calendar.MONTH, NUM ); 
        return calendar.getTime (); 
    } 

    / ** 
     * add and subtract operations on the date specified number of days 
     * @param dATE 
     * @param negative integer positive integer NUM 
     * @return 
     * / 
    public static calculateDateOfDay a date (dATE a date, integer NUM) { 
        Calendar Calendar Calendar.getInstance = (); 
        calendar.setTime (DATE);
        calendar.add(Calendar.DAY_OF_MONTH,num);
        return calendar.getTime();
    }

    public static void main(String[] args) throws ParseException {

        System.out.println(datetimeToString(getMonthStartDate(sdf.parse("2019-12-04 12:09:52"))));
        System.out.println(datetimeToString(getEndWeekDate(sdf.parse("2019-12-04 12:09:52"))));
        System.out.println(datetimeToString(calculateDateOfYear(stringToDatetime("2019-12-04 12:09:52"),-2)));
    }
}