java - 日历方法

Question

除了内置函数，我们是否可以使用任何简单的公式来计算给定月份和年份作为输入的月份的开始日期？

Answer 1

是 - 使用 Calendar 对象:

Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, 2009)
cal.set(Calendar.MONTH, Calendar.JUNE) //0-based so that Calendar.JANUARY is 0
cal.set(Calendar.DAY_OF_MONTH, 1)

然后:

cal.get(Calendar.DAY_OF_WEEK); //is Calendar.MONDAY

因此您可以轻松地为此编写一个方法:

/** takes a 1-based month so that Jjanuary is 1 */
public int getDayAtStart(int year, int month) {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.YEAR, year)
    cal.set(Calendar.MONTH, month - 1);
    cal.set(Calendar.DAY_OF_MONTH, 1);
    return cal.get(Calendar.DAY_OF_WEEK); 
}