java date of acquisition, first of every month, every Monday

java date of acquisition, first of every month, every Monday 

package info.lumanman.h5.util;

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

public class DateUtil {

    public static void main(String[] args) {
       SimpleDateFormat sdf= new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        //addDay(sdf,10);
        // getWeekDay (sdf);
       getMonth(sdf);

   }
    /**
    * Increase the number of days
    * @param sdf
    */
    public static void addDay(SimpleDateFormat sdf,int days){

        // Get Calendar example, java package performance, private constructor Calendar class object is created by the static method
       Calendar calendar=Calendar.getInstance();
        // get the current time and format
       . The System Out.println ( "Current Time:" + sdf.format (calendar.getTime () ));

        // plus the number of days to the current time and outputs days, where the first parameter can be the following three
       Calendar calendar1=Calendar.getInstance();
       calendar1. add(Calendar.DAY_OF_YEAR, days);
       . The System Out.println ( "plus" + Days + "time after day:" + sdf.format (calendar1.getTime () ));

       Calendar calendar2=Calendar.getInstance();
       calendar2. add(Calendar.DAY_OF_MONTH, days);
       . The System Out.println ( "plus" + Days + "time after:" + sdf.format (calendar2.getTime () ));

       Calendar calendar3=Calendar.getInstance();
       calendar3. add(Calendar.DAY_OF_WEEK, days);
       . The System Out.println ( "plus" + Days + "time after:" + sdf.format (calendar3.getTime () ));
   }
    /**
    * Get the current week, a week ago, after the first day and the last day of the week
    * @param sdf
    */
    public static void getWeekDay(SimpleDateFormat sdf){
        // Get Calendar example, java package performance, private constructor Calendar class object is created by the static method
       Calendar calendar=Calendar.getInstance();
        // get the current time and format
       . The System Out.println ( "Current Time:" + sdf.format (calendar.getTime () ));

        // Monday
       Calendar calendar1=Calendar.getInstance();
       calendar1. set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
       System. Out.println ( "Monday:" + sdf.format (calendar1.getTime () ));
        // Sunday
       Calendar calendar2=Calendar.getInstance();
        // foreign Sunday and we are not one week (Sunday through Saturday are foreign to one week)
       calendar2. add(Calendar.DAY_OF_WEEK, 7);
       calendar2. set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
       . System out.println ( "Sunday:" + sdf.format (calendar2.getTime () ));

        //Next Mon
       Calendar calendar3=Calendar.getInstance();
       calendar3. add(Calendar.DAY_OF_MONTH, 7);
       calendar3. set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
       . The System Out.println ( "Monday:" + sdf.format (calendar3.getTime () ));
        // next Sunday
       Calendar calendar4=Calendar.getInstance();
       calendar4. add(Calendar.DAY_OF_MONTH, 14);
       calendar4. set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
       . System out.println ( "next Sunday:" + sdf.format (calendar4.getTime () ));

        //last Monday
       Calendar calendar5=Calendar.getInstance();
       calendar5. add(Calendar.DAY_OF_YEAR, -7);
       calendar5. set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
       . System out.println ( "last Monday:" + sdf.format (calendar5.getTime () ));
        // on Sunday
       Calendar calendar6=Calendar.getInstance();
       calendar6. set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
       . System out.println ( "on Sunday:" + sdf.format (calendar6.getTime () ));
   }
    /**
    * Get the current month, the previous month, the first day after the last day of the month
    * @param sdf
    */
    public static void getMonth(SimpleDateFormat sdf){
        // define the total number of days of the current month, such as 30,31,28,29
        int maxCurrentMonthDay=0;
       Calendar calendar=Calendar.getInstance();
       . The System Out.println ( "Current Time:" + sdf.format (calendar.getTime () ));

        // One month
       Calendar calendar1=Calendar.getInstance();
       calendar1. set(Calendar.DAY_OF_MONTH, 1);
       . The System Out.println ( "the first day of the month:" + sdf.format (calendar1.getTime () ));
        // the last day of the month
       Calendar calendar2=Calendar.getInstance();
       maxCurrentMonthDay=calendar2.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar2. set(Calendar.DAY_OF_MONTH, maxCurrentMonthDay);
       . System out.println ( "the last day of this month:" + sdf.format (calendar2.getTime () ));

        // One month
       Calendar calendar3=Calendar.getInstance();
       maxCurrentMonthDay=calendar3.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar3. add(Calendar.DAY_OF_MONTH, maxCurrentMonthDay);
       calendar3. set(Calendar.DAY_OF_MONTH, 1);
       . The System Out.println ( "the first day of the next month:" + sdf.format (calendar3.getTime () ));
        // the last day of next month
       Calendar calendar4=Calendar.getInstance();
       maxCurrentMonthDay=calendar4.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar4. add(Calendar.DAY_OF_MONTH, maxCurrentMonthDay);
        // The first maxCurrentMonthDay get the number of days of the month, the second maxCurrentMonthDay get the number of days of the next month
       maxCurrentMonthDay=calendar4.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar4. set(Calendar.DAY_OF_MONTH, maxCurrentMonthDay);
       . The System Out.println ( "the first day of the next month:" + sdf.format (calendar4.getTime () ));

        // One month
       Calendar calendar5=Calendar.getInstance();
       maxCurrentMonthDay=calendar5.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar5. add(Calendar.DAY_OF_MONTH, -maxCurrentMonthDay);
       calendar5. set(Calendar.DAY_OF_MONTH, 1);
       . The System Out.println ( "the first day of the month:" + sdf.format (calendar5.getTime () ));
        // the last day of last month
       Calendar calendar6=Calendar.getInstance();
       maxCurrentMonthDay=calendar6.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar6. add(Calendar.DAY_OF_MONTH, -maxCurrentMonthDay);
        // The first maxCurrentMonthDay get the number of days of the month, the second maxCurrentMonthDay get the number of days last month
       maxCurrentMonthDay=calendar6.getActualMaximum(Calendar.DAY_OF_MONTH);
       calendar6. set(Calendar.DAY_OF_MONTH, maxCurrentMonthDay);
       . The System Out.println ( "the first day of the month:" + sdf.format (calendar6.getTime () ));

   }