Learn Java's Date Calendar Date operations

This article introduces the date related operations in the Java development process. The code Shared is as follows:

package jse;
 
import java.io.UnsupportedEncodingException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
 

public class TestDate
{
  public static void main(String[] args) throws ParseException, UnsupportedEncodingException
  {
    Calendar cal = Calendar.getInstance();
//   cal.add(Calendar.DAY_OF_MONTH, -48);
    System.out.println(dateToString(cal));
  }
   
  
  public static String dateToString(Date date)
  {
//SimpleDateFormat = new SimpleDateFormat("y year MM month dd E HH MM minutes ss seconds ", Locale.CHINA);
//SimpleDateFormat = new SimpleDateFormat("y, M, d, E, H, M minutes and s seconds ", location.china);
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.CHINA); // example
    return sdf.format(date);
  }
   
  
  public static String dateToString(Calendar cal)
  {
    return dateToString(cal.getTime());
  }
 
  
  public static Calendar dateStringToCalendar(String dateStr) throws ParseException
  {
//   Calendar cal = Calendar.getInstance();
//   cal.clear();
//   cal.set(Integer.parseInt(date.substring(0, 4)), Integer.parseInt(date.substring(5, 7)) - 1,
//       Integer.parseInt(date.substring(8, 10)));
//   return cal;
     
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    Date date = sdf.parse(dateStr);
    Calendar cal = Calendar.getInstance();
    cal.setTime(date);
    return cal;
  }
 
  
  public static Date dateStringToDate(String date) throws ParseException
  {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    return sdf.parse(date);
  }
 
  
  public static Calendar dateToCalendar(Date date)
  {
    Calendar c1 = Calendar.getInstance();
    c1.setTime(date);
    return c1;
  }
 
  
  public static Date CalendarToDate(Calendar cal)
  {
    return cal.getTime();
  }
 
  
  public int[] calculateDifferDay(Date d1, Date d2)
  {
    Calendar c1 = Calendar.getInstance();
    c1.setTime(d1);
    Calendar c2 = Calendar.getInstance();
    c1.setTime(d2);
    return calculateDifferDay(c1, c2);
  }
 
  
  public int[] calculateDifferDay(Calendar c1, Calendar c2)
  {
    int[] p1 = { c1.get(Calendar.YEAR), c1.get(Calendar.MONTH), c1.get(Calendar.DAY_OF_MONTH) };
    int[] p2 = { c2.get(Calendar.YEAR), c2.get(Calendar.MONTH), c2.get(Calendar.DAY_OF_MONTH) };
    System.out.println("p1[0]=" + p1[0] + " p1[1]=" + p1[1] + " p1[2]=" + p1[2]);
    System.out.println("p2[0]=" + p2[0] + " p2[1]=" + p2[1] + " p2[2]=" + p2[2]);
    int year = p2[0] - p1[0];
    int month = (p2[0] * 12) + p2[1] - ((p1[0] * 12) + p1[1]);
    int day = (int) ((c2.getTimeInMillis() - c1.getTimeInMillis()) / (24 * 60 * 60 * 1000));
    return new int[] { year, month, day };
  }
 
  
  public static Calendar getLastDayOfWeek(Calendar c)
  {
//SimpleDateFormat 2 = new SimpleDateFormat("y, M, d, E, H, M minutes and s seconds ", location.china);
//Println (" current time :" + format2. Format (c.formattime ()));
    c.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
//Println (" Monday time :" + format2. Format (c.formattime ()));
    return c;
  }
 
  
  public static Calendar addOrDecreaseDay(Calendar c, int day)
  {
    c.add(Calendar.DAY_OF_MONTH, day);
    return c;
  }
 
  
  public static int getLastDayOfMonth(int year, int month)
  {
    Calendar c = Calendar.getInstance();
    c.set(year, month - 1, 1);
    return c.getActualMaximum(Calendar.DAY_OF_MONTH);
  }
   
  
  public static int getLastDayOfMonth(Calendar cal)
  {
    return cal.getActualMaximum(Calendar.DAY_OF_MONTH);
  }
   
}