如何在Java中获取给定周数的第一天

问题描述

让我解释一下.通过知道日期的周数和年份:

Let me explain myself. By knowing the week number and the year of a date:

Date curr = new Date();
Calendar cal = Calendar.getInstance();
cal.setTime(curr);
int nweek = cal.WEEK_OF_YEAR;
int year = cal.YEAR;

但现在我不知道如何获取该周第一天的日期.我一直在寻找日历、日期、日期格式，但没有什么有用的...

But now I don't know how to get the date of the first day of that week. I've been looking in Calendar, Date, DateFormat but nothing that may be useful...

有什么建议吗?(在 Java 中工作)

Any suggestion? (working in Java)

推荐答案

那些字段不返回值.这些是constants，用于标识Calendar 对象中您可以获取/设置/添加的字段.要实现你想要的，你首先需要得到一个Calendar，清除它并设置已知值.它会自动将日期设置为该周的第一天.

Those fields does not return the values. Those are constants which identifies the fields in the Calendar object which you can get/set/add. To achieve what you want, you first need to get a Calendar, clear it and set the known values. It will automatically set the date to first day of that week.

// We know week number and year.
int week = 3;
int year = 2010;

// Get calendar, clear it and set week number and year.
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.set(Calendar.WEEK_OF_YEAR, week);
calendar.set(Calendar.YEAR, year);

// Now get the first day of week.
Date date = calendar.getTime();

请学习阅读 javadocs 学习如何使用类/方法/字段，不要尝试在你的 IDE 中随意戳 ;)

Please learn to read the javadocs to learn how to use classes/methods/fields and do not try to poke random in your IDE ;)

也就是说，java.util.Date 和 java.util.Calendar 是 史诗般的失败.如果可以，请考虑切换到 Joda Time.

That said, the java.util.Date and java.util.Calendar are epic failures. If you can, consider switching to Joda Time.

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