日期Date帮助类/日历Calendar的使用

1.DateTime.cs

package com.test;

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

public class DateTime
{
    private DateTime(){}
    
    // 日期格式化
    public static String dateToString(Date date,String format)
    {
        SimpleDateFormat sd = new SimpleDateFormat(format);
        return sd.format(date);
    }
    
    // 字符串转日期
    public static Date strToDate(String str,String format) throws ParseException
    {
        SimpleDateFormat sd = new SimpleDateFormat(format);
        Date d = sd.parse(str);
        return d;
    }
    
    public static String Now()
    {
        Date d = new Date();
        return DateTime.dateToString(d,"yyyy-MM-dd HH:mm:ss");
    }
}

2.使用

package com.test;
import java.text.ParseException;
import java.util.Calendar;
import java.util.Date;
 
public class Test {
     
    public static void main(String[] args) throws ParseException {
        Date d = new Date();
        // 日期格式化
        String s = DateTime.dateToString(d,"yyyy-MM-dd HH:mm:ss");
        System.out.println(s);
        // 获取当前时间
        System.out.println(DateTime.Now());
        // 字符串转日期
        Date dd = DateTime.strToDate("2022-03-29 21:59:58", "yyyy-MM-dd HH:mm:ss");
        System.out.println(dd);
         
        // 日历
        Calendar c = Calendar.getInstance();
        c.add(Calendar.YEAR, -3); // 3年前
        c.set(2022, 03, 15); // 设置时间
        int year = c.get(Calendar.YEAR);
        int month = c.get(Calendar.MONTH) + 1;
        int date = c.get(Calendar.DATE);
        System.out.println(year + "-" + month + "-" + date);
         
    }
 
}