Java时间相关类Date、DateFormat、SimpleDateFormat、Calendar

    	long currentTime = System.currentTimeMillis(); //当前时刻毫秒数
    	System.out.println(currentTime);
    
    
    java
    
    

    	Date date = new Date();
    	System.out.println(date);
    System.out.println(date.getTime());
    
    
    java
    
    

    //yyyy-MM-dd hh:mm:ss  标准格式：年-月-日 时:分:秒
    //把时间对象转换为指定格式的字符串
    	SimpleDateFormat simpleDateFormat1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
    	String datetime = simpleDateFormat1.format(new Date());
    	System.out.println(datetime);  //结果：2021-02-23 11:06:56
    	//把指定格式的字符串转换为时间对象
    	Date date = simpleDateFormat1.parse(datetime);
    	System.out.println(date);      //结果：Tue Feb 23 11:06:56 CST 2021
    
    
    java
    
    

    	//年 月 日 时 分 秒
    	GregorianCalendar gregorianCalendar =
                new GregorianCalendar(2021,Calendar.FEBRUARY,4,15,52,23);
    	int year = gregorianCalendar.get(Calendar.YEAR);
    	int month = gregorianCalendar.get(Calendar.MONTH);
    	int day = gregorianCalendar.get(Calendar.DATE);
    	int week = gregorianCalendar.get(Calendar.DAY_OF_WEEK);
       	System.out.println(year);  //2021
    System.out.println(month); //1
    System.out.println(day);   //4
    System.out.println(week);  //5
    
    
    java
    
    
![](https://ad.itadn.com/c/weblog/blog-img/images/2025-07-12/oUvdJsn4WYSbE8BtINFPA729k3CL.png)

    	gregorianCalendar.set(Calendar.YEAR, 2022);
    	gregorianCalendar.set(Calendar.MONTH, Calendar.DECEMBER);
    	gregorianCalendar.set(Calendar.DATE, 1);
    	gregorianCalendar.set(Calendar.HOUR_OF_DAY, 1);
    	gregorianCalendar.set(Calendar.MINUTE, 1);
    	gregorianCalendar.set(Calendar.SECOND, 1);
    
    //计算传入日期往后7天是几号
    gregorianCalendar.add(Calendar.DATE, +7);
    
    
    java
    
    

    	//日历对象和时间对象转换
    Date date = gregorianCalendar.getTime();
    System.out.println(date);
    gregorianCalendar.setTime(new Date());
    
    
    java