JDK1.8之前

使用Date

System.out.println(System.currentTimeMillis());
        //java.util.date
        Date date = new Date();
        System.out.println(date);
        System.out.println(date.toString());
        System.out.println(date.getTime());
        //java.sql.date
        java.sql.Date date1 = new java.sql.Date(date.getTime());
        System.out.println(date1);
        System.out.println(date1.toString());
        System.out.println(date1.getTime());

使用SimpleDateFormat来格式化Date

       //simpledateformat
        SimpleDateFormat sdf = new SimpleDateFormat();
        //格式化日期
        String str_date = sdf.format(new Date());
        System.out.println(str_date);
        //解析
        Date date2 = sdf.parse(str_date);
        System.out.println(date2);

        //按指定格式格式化
        SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd");
        String str_date2 = sdf2.format(new Date());
        System.out.println(str_date2);
        //解析
        Date date3 = sdf2.parse(str_date2);
        System.out.println(date3);

Calendar类

@Test
    public void CalenderTest(){
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(new Date(99,10,31));
        //getTime()
        System.out.println(calendar.getTime());
        //
        System.out.println(calendar.get(Calendar.DAY_OF_WEEK));//周日为1，周一为2
        System.out.println(calendar.get(Calendar.DAY_OF_YEAR));
        //
        calendar.set(Calendar.DAY_OF_YEAR,1);
        System.out.println(calendar.get(Calendar.DAY_OF_YEAR));

        calendar.add(Calendar.DAY_OF_YEAR,10);
        System.out.println(calendar.get(Calendar.DAY_OF_YEAR));

        //localtime localdate localdatetime
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(localDateTime);
    }

Calender是一个抽象类，无法直接new一个对象。使用Calendar.getInstance（）或者 new GregorianCalendar()来创建

JDK1.8中

JDK1.8日期使用