Java函数2:计算两个日期相差的天数

import java.util.Scanner;
public class HelloWorld {
	public static void main(String[] args){
	//	Scanner s = new Scanner(System.in);
	//	System.out.println("请输入一个数字");
	//	int num = s.nextInt();
		int SUM = Caluater_date_sub_day(2009,1,25,2008,1,10);
		System.out.println(SUM);
	}
	//判断闰年平年
	public static boolean isLeap(int y){
		if((y % 4 == 0 && y % 100 != 0) || y % 400 == 0)
			return true ;
		return false ;
	}
	//判断一年已经过了多少天
	public static int GetDay(int y , int m , int d){
		int sum = 0 ;
		switch(m){
		case 12 : sum += 31 ;
		case 11 : sum += 30 ;
		case 10 : sum += 31 ;
		case 9  : sum += 30 ;
		case 8  : sum += 31 ;
		case 7  : sum += 31 ;
		case 6  : sum += 30 ;
		case 5  : sum += 31 ;
		case 4  : sum += 30 ;
		case 3  : sum += 31 ;
		case 2  :
				if(isLeap(y) == true)
					sum += 29 ;
				else
					sum += 28 ;
		case 1  : sum += 31 ;
		sum += d ;
		}
		return d ;
	}
	//判断一年还剩下多少天
	public static int OthearDay(int y , int m , int d)
	{
		if(isLeap(y) == true)
		   return 366 - GetDay(y , m , d);
		return 365 - GetDay(y, m, d) ;
	}
	//判断两个日期相差的天数
	public static int Caluater_date_sub_day(int y1,int m1,int d1,int y2,int m2 ,int d2)
	{
		if(y1 == y2){
			int day1 = GetDay(y1, m1, d1) - GetDay(y2, m2, d2) ;
			return abs(day1);
		}
		else if(y1 < y2){
			int sum1 = OthearDay(y1, m1, d1) ;
			int sum2 = GetDay(y2, m2, d2) ;
			int sum3 = 0 ;
			for(int i = y1 + 1 ; i < y2 ; i++){
				if(isLeap(i))
					sum3+=366 ;
				else
					sum3+=365 ;
			}
			return sum1+sum2+sum3 ;
		}else
		{
			int sum1 = GetDay(y1, m1, d1) ;
			int sum2 = OthearDay(y2, m2, d2) ;
			int sum3 = 0 ;
			for(int i = y2 + 1 ; i < y1 ; i++){
				if(isLeap(i))
					sum3+=366 ;
				else
					sum3+=365 ;
			}
			return sum1+sum2+sum3 ;
		}
	}
	//计算一个数的绝对值
	public static int abs(int num){
		return num > 0 ? num : -num ;
	}
}