日期计算算法java

日期计算在Java中通常使用java.util.Calendar类进行实现。通过该类，可以计算两个日期之间的天数、月数、年数等。下面是一些基本的日期计算方法：

1. 计算两个日期之间的天数

Calendar cal1 = Calendar.getInstance();
cal1.set(2019, 8, 1);
Calendar cal2 = Calendar.getInstance();
cal2.set(2019, 8, 10);
long diff = cal2.getTimeInMillis() - cal1.getTimeInMillis();
long days = diff / (24 * 60 * 60 * 1000);
System.out.println("Days between two dates: " + days);

2. 计算两个日期之间的月数

Calendar cal1 = Calendar.getInstance();
cal1.set(2019, 8, 1);
Calendar cal2 = Calendar.getInstance();
cal2.set(2020, 3, 10);
int months = (cal2.get(Calendar.YEAR) - cal1.get(Calendar.YEAR)) * 12
        + cal2.get(Calendar.MONTH) - cal1.get(Calendar.MONTH);
System.out.println("Months between two dates: " + months);

3. 计算两个日期之间的年数

Calendar cal1 = Calendar.getInstance();
cal1.set(2019, 8, 1);
Calendar cal2 = Calendar.getInstance();
cal2.set(2021, 8, 1);
int years = cal2.get(Calendar.YEAR) - cal1.get(Calendar.YEAR);
System.out.println("Years between two dates: " + years);

4. 计算某个日期加上一定天数后的日期

Calendar cal = Calendar.getInstance();
cal.set(2019, 8, 1);
int daysToAdd = 10;
cal.add(Calendar.DAY_OF_MONTH, daysToAdd);
Date newDate = cal.getTime();
System.out.println("New date: " + newDate);

5. 计算某个日期减去一定天数后的日期

Calendar cal = Calendar.getInstance();
cal.set(2019, 8, 11);
int daysToSubtract = 10;
cal.add(Calendar.DAY_OF_MONTH, -daysToSubtract);
Date newDate = cal.getTime();
System.out.println("New date: " + newDate);