输入某年某月某日，判断这一天是这一年的第几天

代码如下：

package cn.wuhan.unit7;
import java.util.*;

public class Tianshu2 {
	public static void main(String[] args) {
		int year,month,day;
		int days=0;
		int dayCount=0;
		Scanner sc;
		boolean isTrue=false;
		do{
			isTrue=false;
			System.out.println("输入某年某月某日，判断这一天是这一年的第几天?");
			System.out.println("请输入年: ");
			sc = new Scanner(System.in);
			year = sc.nextInt();
			System.out.println("请输入月：");
			sc = new Scanner(System.in);
			month = sc.nextInt();
			System.out.println("请输入日：");
			sc = new Scanner(System.in);
			day = sc.nextInt();
			//数据输入错误
			if(year<=0||month<=0||month>12||day<=0||day>31){
				System.out.println("输入的数据有误，请重新输入!");
				isTrue = true;
			}
		}while(isTrue);
		
		for(int i=1;i<month;i++){
			switch(i){
			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:
				if((year%400==0)||((year%4==0)&&(year%100!=0))){
					days=29;
				}else{
					days=28;
				}
				break;
				
			}
			dayCount += days;
		}
		
		dayCount += day;
		System.out.println(year+"年"+month+"月"+day+"日，是这一年的第"+dayCount+"天");
		
	}

}

效果如下：