4. java.util.Calendar( 日历)类 类
 Calendar是一个抽象基类，主用用于完成日期字段之间相互操作的功能。
 获取Calendar实例的方法
 使用Calendar.getInstance()方法
 调用它的子类GregorianCalendar的构造器。
 一个Calendar的实例是系统时间的抽象表示，通过get(int field)方法来取得想
要的时间信息。比如YEAR、MONTH、DAY_OF_WEEK、HOUR_OF_DAY 、
MINUTE、SECOND
 public void set(int field,int value)
 public void add(int field,int amount)
 public final Date getTime()
 public final void setTime(Date date)
 注意:
 获取月份时：一月是0，二月是1，以此类推，12月是11
 获取星期时：周日是1，周二是2 ， 。。。。周六是7

/*
    Calendar日历类(抽象类）的使用

     */
    @Test
    public void testCalendar(){
        //1.实例化
        //方式一：创建其子类（GregorianCalendar）的对象
        //方式二：调用其静态方法getInstance()
        Calendar calendar = Calendar.getInstance();
//        System.out.println(calendar.getClass());

        //2.常用方法
        //get()
        int days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);
        System.out.println(calendar.get(Calendar.DAY_OF_YEAR));

        //set()
        //calendar可变性
        calendar.set(Calendar.DAY_OF_MONTH,22);
        days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);

        //add()
        calendar.add(Calendar.DAY_OF_MONTH,-3);
        days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);

        //getTime():日历类---> Date
        Date date = calendar.getTime();
        System.out.println(date);

        //setTime():Date ---> 日历类
        Date date1 = new Date();
        calendar.setTime(date1);
        days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);

    }
}

 

 

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