用Java计算闰年

Question

可能重复:
用于计算闰年的Java代码,此代码是否正确？

这是作业,我已经收到了我的成绩,但我没有在我的代码中实现闰年.这是一个简单的程序,可根据用户输入显示一个月内的数字.唯一的问题是我无法弄清楚实现闰年的方法是在2月而不是28天获得29天,而不需要写多个if语句.当然有一种更简单的方法吗？这是代码:

//Displays number of days in a month

package chapter_3;

import java.util.Scanner;


public class Chapter_3 {

    public static void main(String[] args) {
        System.out.println("This program will calculate \n"
                + "the number of days in a month based upon \n"
                + "your input, when prompted please enter \n"
                + "the numerical value of the month you would like\n"
                + "to view including the year. Example: if you would like\n"
                + "to view March enter 3 2011 and so on.");

        Scanner input = new Scanner(System.in);

        //Prompt user for month and year
        System.out.print("Please enter the month and year: ");
        int month = input.nextInt();
        int year = input.nextInt();

        if (month == 1) {
            System.out.println("January " + year + " has 31 days");
        }   
        else if (month == 2) {
            System.out.println("February " + year + " has 28 days");
        }   
        else if (month == 3) {
            System.out.println("March " + year + " has 31 days");
        }
        else if (month == 4) {
            System.out.println("April " + year + " has 30 days");
        }
        else if (month == 5) {
            System.out.println("May " + year + " has 31 days");
        }
        else if (month == 6) {
            System.out.println("June " + year + " has 30 days");
        }
        else if (month == 7) {
            System.out.println("July " + year + " has 31 days");
        }
        else if (month == 8) {
            System.out.println("August " + year + " has 31 days");
        }
        else if (month == 9) {
            System.out.println("September " + year + " has 30 days");
         }
        else if (month == 10) {
            System.out.println("October " + year + " has 30 days");
        }
        else if (month == 11) {
            System.out.println("November " + year + " has 30 days");
        }
        else if (month == 12) {
            System.out.println("December " + year + " has 31 days");
         }
        else {
            System.out.println("Please enter the numerical value "
                + "of the month you would like to view");
        }
    }
}        

Answer 1

如果你使用GregorianCalendar,你可以这样做

确定给定年份是否为闰年.如果给定年份是闰年,则返回true.要指定BC年份数,必须给出1年的数字.例如,BC 4年被指定为-3.

GregorianCalendar cal = new GregorianCalendar();

if(cal.isLeapYear(year))
{
    System.out.print("Given year is leap year.");
}
else
{ 
    System.out.print("Given year is not leap year.");
}

Answer 2

引用http://en.wikipedia.org/wiki/Leap_year

可以被100整除的年份不是闰年,除非它们也可以被400整除,在这种情况下它们是闰年.

所以,如果你想重新发明轮子:

boolean isLeapYear = year%4 == 0 && (year%100 != 0 || year%400 == 0)

但最优雅的解决方案(取自此处)可能就是

public static boolean isLeapYear(int year) {
  Calendar cal = Calendar.getInstance();
  cal.set(Calendar.YEAR, year);
  return cal.getActualMaximum(DAY_OF_YEAR) > 365;
}