java得到当月天数

1.使用calendar类实现

	/**
	 * 取得当月天数
	 * */
	public static int getCurrentMonthLastDay()
	{
		Calendar a = Calendar.getInstance();
		a.set(Calendar.DATE, 1);//把日期设置为当月第一天
		a.roll(Calendar.DATE, -1);//日期回滚一天，也就是最后一天
		int maxDate = a.get(Calendar.DATE);
		return maxDate;
	}

	/**
	 * 得到指定月的天数
	 * */
	public static int getMonthLastDay(int year, int month)
	{
		Calendar a = Calendar.getInstance();
		a.set(Calendar.YEAR, year);
		a.set(Calendar.MONTH, month - 1);
		a.set(Calendar.DATE, 1);//把日期设置为当月第一天
		a.roll(Calendar.DATE, -1);//日期回滚一天，也就是最后一天
		int maxDate = a.get(Calendar.DATE);
		return maxDate;
	}

2.使用自己编写的函数实现

package test;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

/**
 * 日期工具类 by hpf 
 * */
public class DateUtils
{
	//返回当前年月日
	String getNowDate()
	{
		Date date = new Date();
		String nowDate = new SimpleDateFormat("yyyy年MM月dd日").format(date);
		return nowDate;
	}

	//返回当前年份
	int getYear()
	{
		Date date = new Date();
		String year = new SimpleDateFormat("yyyy").format(date);
		return Integer.parseInt(year);
	}

	//返回当前月份
	int getMonth()
	{
		Date date = new Date();
		String month = new SimpleDateFormat("MM").format(date);
		return Integer.parseInt(month);
	}

	//判断闰年
	boolean isLeap(int year)
	{
		if (((year % 100 == 0) && year % 400 == 0) || ((year % 100 != 0) && year % 4 == 0))
			return true;
		else
			return false;
	}

	//返回当月天数
	int getDays(int year, int month)
	{
		int days;
		int FebDay = 28;
		if (isLeap(year))
			FebDay = 29;
		switch (month)
		{
			case 1:
			case 3:
			case 5:
			case 7:
			case 8:
			case 10:
			case 12:
				days = 31;
				break;
			case 4:
			case 6:
			case 9:
			case 11:
				days = 30;
				break;
			case 2:
				days = FebDay;
				break;
			default:
				days = 0;
				break;
		}
		return days;
	}

	//返回当月星期天数
	int getSundays(int year, int month)
	{
		int sundays = 0;
		SimpleDateFormat sdf = new SimpleDateFormat("EEEE");
		Calendar setDate = Calendar.getInstance();
		//从第一天开始
		int day;
		for (day = 1; day <= getDays(year, month); day++)
		{
			setDate.set(Calendar.DATE, day);
			String str = sdf.format(setDate.getTime());
			if (str.equals("星期日"))
			{
				sundays++;
			}
		}
		return sundays;
	}

	public static void main(String[] args)
	{
		DateUtils du = new DateUtils();
		System.out.println("今天日期是：" + du.getNowDate());
		System.out.println("本月有" + du.getDays(du.getYear(), du.getMonth()) + "天");
		System.out.println("本月有" + du.getSundays(du.getYear(), du.getMonth()) + "个星期天");
	}
}