感謝原文作者：https://www.oreilly.com/library/view/java-cookbook/0596001703/ch06s11.html

1、問題
現有一個日期，需要查詢該日期的星期幾，月份或年份。

2、解決方法
使用Calendar類的get（）方法，該方法具有用於檢索大多數此類值的常量。

3、討論
Calendar類可以返回大部分內容：

// CalendarDemo.java
Calendar c = Calendar.getInstance(  );    // today
System.out.println("Year: " + c.get(Calendar.YEAR));
System.out.println("Month: " + c.get(Calendar.MONTH));
System.out.println("Day: " + c.get(Calendar.DAY_OF_MONTH));
System.out.println("Day of week = " + c.get(Calendar.DAY_OF_WEEK));
System.out.println("Day of year = " + c.get(Calendar.DAY_OF_YEAR));
System.out.println("Week in Year: " + c.get(Calendar.WEEK_OF_YEAR));
System.out.println("Week in Month: " + c.get(Calendar.WEEK_OF_MONTH));
System.out.println("Day of Week in Month: " + 
            c.get(Calendar.DAY_OF_WEEK_IN_MONTH));
System.out.println("Hour: " + c.get(Calendar.HOUR));
System.out.println("AM or PM: " + c.get(Calendar.AM_PM));
System.out.println("Hour (24-hour clock): " + 
            c.get(Calendar.HOUR_OF_DAY));
System.out.println("Minute: " + c.get(Calendar.MINUTE));
System.out.println("Second: " + c.get(Calendar.SECOND));
 

4、控制檯列印

Year: 2018
Month: 10
Day: 20
Day of week = 3
Day of year = 324
Week in Year: 47
Week in Month: 4
Day of Week in Month: 3
Hour: 9
AM or PM: 0
Hour (24-hour clock): 9
Minute: 44
Second: 58