JDK源码阅读-------自学笔记(十四)(java.util.Calendar日历类)

Calendar

• 提供了关于日期计算的相关功能，比如：年、月、日、时、分、秒的展示和计算。
• GregorianCalendar 是 Calendar 的一个具体子类，提供了世界上大多数国家/地区使用的标准日历系统
• 所在包java.util.Calendar

实战

• 初始化
  

     Calendar calendar = new GregorianCalendar();

• 打印结果
  

          Calendar calendar = new GregorianCalendar(3000, 12, 12, 15, 31, 42);
  
          System.out.println(calendar);

• 获取对象的值
  

          Calendar calendar = new GregorianCalendar(3000, 12, 12, 06, 31, 42);
  
          StringBuilder stringBuilder = new StringBuilder();
  
          stringBuilder.append(calendar.get(Calendar.YEAR));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.MONTH));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.DATE));
  
          System.out.println(stringBuilder.toString());

注:
    参数表示 日：Calendar.DATE和Calendar.DAYOFMONTH同义 星期几：1-7.(周日是1，周一是2......周六是7)

• 设置日期
  

          Calendar calendar = new GregorianCalendar();
  
          calendar.set(Calendar.YEAR,10000);
          calendar.set(Calendar.MONTH,10);
          calendar.set(Calendar.DATE,15);
  
          StringBuilder stringBuilder = new StringBuilder();
  
          stringBuilder.append(calendar.get(Calendar.YEAR));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.MONTH));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.DATE));
  
          System.out.println(stringBuilder.toString());

• 日期的计算
  

          Calendar calendar = new GregorianCalendar();
  
          // 往后300天后的日期
          calendar.add(Calendar.DATE,300);
  
  
          StringBuilder stringBuilder = new StringBuilder();
  
          stringBuilder.append(calendar.get(Calendar.YEAR));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.MONTH));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.DATE));
  
          System.out.println(stringBuilder.toString());

• 日期对象和时间对象的转化
  

  public static void main(String[] args) throws ParseException {
  
          Calendar calendar = new GregorianCalendar();
  
          Date date = calendar.getTime();
          System.out.println("日历转日期:"+"
  "+date);
  
          Calendar calendar1 = new GregorianCalendar();
          calendar1.setTime(new Date());
  
          System.out.println("日期转日历:");
          printYearAndMonthAndDay(calendar1);
  
      }
  
      private static void printYearAndMonthAndDay(Calendar calendar) {
          StringBuilder stringBuilder = new StringBuilder();
  
          stringBuilder.append(calendar.get(Calendar.YEAR));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.MONTH));
          stringBuilder.append("-");
          stringBuilder.append(calendar.get(Calendar.DATE));
  
          System.out.println(stringBuilder.toString());
      }

• 编写程序，利用GregorianCalendar类，打印当前月份的日历，今天的日期是 2017-05-18

样式:

                    

代码:

    public static void main(String[] args) {

        //输入日期处理
        String printClientDate = getPrintClientDate();

        try {
            // 日期格式化
            Calendar c = getFormatCalendar(printClientDate);

            //获取月份中的哪一天
            int day = c.get(Calendar.DAY_OF_MONTH);

            // 获取日期最大值
            int days = c.getActualMaximum(Calendar.DATE);

            //第一行周数空格的打印
            getWeekResult(c);

            //输出月份内日期
            getDateResult(c, day, days);

        } catch (ParseException e) {
            e.printStackTrace();
        }
    }

    /**
     * 获取日期返回结果
     *
     * @param c    输入日期对像
     * @param day  当前输入的天数
     * @param days 输入的月最多多少天
     */
    private static void getDateResult(Calendar c, int day, int days) {

        for (int i = 1; i <= days; i++) {

            // 打印的天数是否是当前输入的天数,是加*,不是直接打印
            if (day == c.get(Calendar.DAY_OF_MONTH)) {
                //标记输入的天数(即当前输入天)
                System.out.print(c.get(Calendar.DAY_OF_MONTH) + "*	");
            } else {
                System.out.print(c.get(Calendar.DAY_OF_MONTH) + "	");
            }

            // 获取当前日期是周几,如果是周六,就进行换行
            if (c.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY) {
                System.out.println();
            }

            //每次打印完,下次打印前,天数加一天
            c.add(Calendar.DAY_OF_MONTH, 1);

        }
    }

    /**
     * 获取输入周
     *
     * @param c 输入日期
     */
    private static void getWeekResult(Calendar c) {
        System.out.println("日	一	二	三	四	五	六");

        // 当前日期置为1,就是日历的第一天
        c.set(Calendar.DAY_OF_MONTH, 1);

        // 第一行日历根据周几,前边添加几个换行符
        for (int i = 0; i < c.get(Calendar.DAY_OF_WEEK) - 1; i++) {
            System.out.print("	");
        }
    }

    /**
     * 获取日期格式化后
     *
     * @param printClientDate 输入的日期
     * @return 返回日期对象
     * @throws ParseException 产生异常
     */
    private static Calendar getFormatCalendar(String printClientDate) throws ParseException {
        Date date;
        DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        date = df.parse(printClientDate);
        Calendar c = new GregorianCalendar();
        c.setTime(date);

        System.out.println("您刚刚输入的日期是:" + df.format(date));
        return c;
    }

    /**
     * 获取控制台输入日期
     *
     * @return 输入的日期
     */
    private static String getPrintClientDate() {
        System.out.println("请输入日期(格式为:2020-9-10):");
        Scanner scanner = new Scanner(System.in);
        return scanner.nextLine();
    }

注:

       JDK8,已经推出了新的取代的新方案,

详情查阅 https://www.cnblogs.com/liuyangfirst/p/11257602.html