我尝试了以下代码：
Calendar c1 = Calendar.getInstance(); c1.set(Calendar.YEAR,0); c1.set(Calendar.DAY_OF_YEAR,1); Date d1 = c1.getTime(); Calendar c2 = Calendar.getInstance(); c2.setTime(d1); c2.set(Calendar.YEAR,2001); c2.set(Calendar.DAY_OF_YEAR,1); System.out.println(c2.getTime().toString()); Calendar c3 = Calendar.getInstance(); c3.set(Calendar.YEAR,2000); c3.set(Calendar.DAY_OF_YEAR,1); Date d2 = c3.getTime(); Calendar c4 = Calendar.getInstance(); c4.setTime(d2); c4.set(Calendar.YEAR,2001); c4.set(Calendar.DAY_OF_YEAR,1); System.out.println(c4.getTime().toString());
结果是：
Wed Jan 01 23:47:00 CET 2001 Mon Jan 01 23:47:00 CET 2001
哪里不对？我不应该以这种方式使用日历设置YEAR？
解决方法
这一年是相对于时代的.通过将年份设置为小于或等于0的日历,日历会通过切换时代(从AD到BC或从BC移动到AD)来自动更正.这种行为从其他领域更为人所知.例如.如果将月份设置为负值,那么年份相应减少.
这些更正不是单独进行的,而是一次性完成,通常当您调用getTime()来读取生成的日期时.
Calendar c1 = Calendar.getInstance(); // August 16th,2012 AD
c1.set(Calendar.YEAR,0); // August 16th,0 AD
c1.set(Calendar.DAY_OF_YEAR,1); // January 1st,0 AD
Date d1 = c1.getTime(); // January 1st,1 BC (corrected)
Calendar c2 = Calendar.getInstance();
c2.setTime(d1);
c2.set(Calendar.YEAR,2001); // January 1st,2001 BC
c2.set(Calendar.DAY_OF_YEAR,1);
System.out.println(c2.getTime()); // prints "Wed Jan 01 05:35:00 CET 2001"
// because 01/01/2001 BC was a Wednesday
因此,不要将年份设定为2001年,您必须将其设置为-2000(因为0年根本不存在).或者你可以明确地设定时代：
c2.set(Calendar.ERA,GregorianCalendar.AD);
解决这个“错误”的另一种方法是在完整日期设置之前不读取时间：
Calendar c1 = Calendar.getInstance(); // August 16th,0 AD c1.set(Calendar.YEAR,2001 AD System.out.println(c1.getTime()); // prints the expected date
要输出日期的时代,您可以在SimpleDateFormat的模式中使用“G”：
new SimpleDateFormat("E MMM dd HH:mm:ss z yyyy G").format(c2.getTime())
// "Wed Jan 01 05:35:00 CET 2001 BC"
