問題描述
我正在嘗試從最初以字符串形式出現的日期中減去 5 天.
I'm trying to subtract 5 days from a date which comes in as a string initially.
我查看了有關此主題的其他一些帖子，但我從代碼中得到的結果總是不正確的.主要問題是，例如，減去天數時，年份值似乎沒有改變 - 2012-01-01 minus 5 days give me 'Jan 27 2012' 使用此代碼 -
I have had a look at some of the other posts on this subject but the result i get from the code is always incorrect. The main problem is that the year value does not seem to change when the days are subtracted for example - 2012-01-01 subtract 5 days gives me 'Jan 27 2012' using this code -
cal.add(Calendar.DATE, -5);
請幫忙.
推薦答案
你知道嗎，在 Java 中，月份 1 實際上是二月?
Did you know that, in Java, month 1 is actually February?
Date februaryTheFirst = new Date(2012,1,1); // equals 2012-02-01
這可以解釋您所看到的.如果你想實例化 2012-01-01 ，你應該這樣做:
This might explain what you are seeing. If you want to instantiate 2012-01-01 instead, you should do:
Date firstDayOf2012 = new Date(2012,0,1); // this is 2012-01-01
在處理 Calendar 時會發生完全相同的事情:
Exactly the same thing happens when dealing with Calendar:
Calendar.getInstance().set(2012,0,1); // 2012-01-01
請務必查看 Date(int, int, int) 的文檔和 Calendar.set(int, int, int).此外，您可以檢查解析字符串的方式.如果您使用 SimpleDateFormat.parse(...)，事情會變得更容易.
Be sure to check the documentation for Date(int, int, int) and Calendar.set(int, int, int). Also, you could check the way you are parsing the string. If you use SimpleDateFormat.parse(...), things can be easier.
很奇怪，不是嗎?想想看……就像一個有趣的事實，IntelliJ 的文檔用 @MagicConstant 注釋了第二個參數月，以提醒程序員發生了一些非常奇怪的事情.
Strange, isn't it? Go figure... Just as a fun fact, IntelliJ's documentation annotates this second parameter, month, with @MagicConstant, to remember the programmer that there's something very strange going on.
這篇關于Java - 從日期中減去天數的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！