java for risc-v系列知识讲座（12）--- Calendar时间处理类

szy

//采用默认时区和语言环境
Calendar calendar = Calendar.getInstance(); //获取或设置时间
System.out.println("年:" + calendar.getWeekYear());
System.out.println("年：" + calendar.get(Calendar.YEAR));
System.out.println("月：" + (calendar.get(Calendar.MONTH)+1)); //只有月分才需要加1 因为月分从0开始计算
System.out.println("日：" + calendar.get(Calendar.DAY_OF_MONTH));
System.out.println("时：" + calendar.get(Calendar.HOUR_OF_DAY));//24小时制
System.out.println("时：" + calendar.get(Calendar.HOUR));//12小时制
System.out.println("分：" + calendar.get(Calendar.MINUTE));
System.out.println("秒：" + calendar.get(Calendar.SECOND));
显示如下：
年:2021
年：2021
月：8
日：16
时：16
时：4
分：32
秒：6


Calendar calendar1 = Calendar.getInstance();
calendar1.set(2021,7,16,0,0,0);
Calendar calendar2 = Calendar.getInstance();
calendar2.set(2021,7,16,0,0,0);
System.out.println(calendar1.getTime());
System.out.println(calendar2.getTime());
System.out.println(calendar2.before(calendar1));
System.out.println( calendar2.after(calendar1));
System.out.println(calendar1.after(calendar2));
System.out.println(calendar1.before(calendar2));
直接Run显示：
Mon Aug 16 00:00:00 CST 2021
Mon Aug 16 00:00:00 CST 2021
false
false
false
false
如果两次getInstance之间延时：
Calendar calendar1 = Calendar.getInstance();
calendar1.set(2021,7,16,0,0,0);
Thread.sleep(10000); //10秒
Calendar calendar2 = Calendar.getInstance();
calendar2.set(2021,7,16,0,0,0);
System.out.println(calendar1.getTime());
System.out.println(calendar2.getTime());
System.out.println(calendar2.before(calendar1));
System.out.println( calendar2.after(calendar1));
System.out.println(calendar1.after(calendar2));
System.out.println(calendar1.before(calendar2));
直接Run显示：
Mon Aug 16 00:00:00 CST 2021
Mon Aug 16 00:00:00 CST 2021
false
false
false
false
但当我在第二个getInstance打上断点,停下来之后再运行时：
Mon Aug 16 00:00:00 CST 2021
Mon Aug 16 00:00:00 CST 2021
true
false
true
false
如果将两个set都注释掉：
Calendar calendar1 = Calendar.getInstance();
//        calendar1.set(2021,7,16,0,0,0);
Thread.sleep(10000);
Calendar calendar2 = Calendar.getInstance();
//        calendar2.set(2021,7,16,0,0,0);
System.out.println(calendar1.getTime());
System.out.println(calendar2.getTime());
System.out.println(calendar2.before(calendar1));
System.out.println( calendar2.after(calendar1));
System.out.println(calendar1.after(calendar2));
System.out.println(calendar1.before(calendar2));
则显示：
Mon Aug 16 16:52:29 CST 2021
Mon Aug 16 16:52:39 CST 2021
false
true
false
true