Code written by a very serious student

package com.qimenguigu.l07131;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * Enter the year, month, day, next|prior, if it is a correct date, calculate the previous or next day
 *
 * @author Longjie
 * @website www.qimenguigu.com
*/
public class Title15 {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		System.out.println("请输入年份");
		String s1 = br.readLine();
		System.out.println("请输入月份");
		String s2 = br.readLine();
		System.out.println("请输入日份");
		String s3 = br.readLine();
		int year = Integer.parseInt(s1);
		int month = Integer.parseInt(s2);
		int day = Integer.parseInt(s3);

		if (year >= 0 && month >= 1 && month <= 12) {
			if (month == 1 || month == 3 || month == 5 || month == 7
					|| month == 8 || month == 10 || month == 12) {
				if (day >= 1 && day <= 31) {
					System.out.println("您输入的日期为:" + year + "年" + month + "月"
							+ day + "日");
					if (day == 31) {
						if (month == 12)
							System.out.println("且上一天为：" + year + "年12月"
									+ (day - 1) + "日" + "," + "下一天为："
									+ (year + 1) + "年1月1日");
						else
							System.out.println("且上一天为：" + year + "年" + month
									+ "月" + (day - 1) + "日" + "," + "下一天为："
									+ year + "年" + (month + 1) + "月1日");
					} else if (day == 1) {
						if (month == 1)
							System.out.println("且上一天为：" + (year - 1)
									+ "年12月31日" + "," + "下一天为：" + year + "年"
									+ month + "月" + (day + 1) + "日");
						else if (month == 3) {
							if ((year % 4 == 0 && year % 100 != 0)
									|| (year % 400 == 0))
								System.out.println("且上一天为：" + year + "年2月29日"
										+ "," + "下一天为：" + year + "年" + month
										+ "月" + (day + 1) + "日");
							else
								System.out.println("且上一天为：" + year + "年2月28日"
										+ "," + "下一天为：" + year + "年" + month
										+ "月" + (day + 1) + "日");
						} else
							System.out.println("且上一天为：" + year + "年"
									+ (month - 1) + "月30日" + "," + "下一天为："
									+ year + "年" + month + "月" + (day + 1)
									+ "日");
					} else
						System.out.println("且上一天为：" + year + "年" + month + "月"
								+ (day - 1) + "日" + "," + "下一天为：" + year + "年"
								+ month + "月" + (day + 1) + "日");
				} else
					System.out.println("您输入的日期不合法");
			} else if (month == 4 || month == 6 || month == 9 || month == 11) {
				if (day >= 1 && day <= 30) {
					System.out.println("您输入的日期为:" + year + "年" + month + "月"
							+ day + "日");
					if (day == 30)
						System.out.println("且上一天为：" + year + "年" + month + "月"
								+ (day - 1) + "日" + "," + "下一天为：" + year + "年"
								+ (month + 1) + "月1日");
					else if (day == 1)
						System.out.println("且上一天为：" + year + "年" + (month - 1)
								+ "月31日" + "," + "下一天为：" + year + "年" + month
								+ (day + 1) + "日");
					else
						System.out.println("且上一天为：" + year + "年" + month + "月"
								+ (day - 1) + "日" + "," + "下一天为：" + year + "年"
								+ month + (day + 1) + "日");
				} else
					System.out.println("您输入的日期不合法");
			}else if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
 if (day == 29)
 System.out.println("The date you entered It is: " + year + "year" + month + "month"
 + day + "day" + "n" + "And the previous day is: " + year + "February 28th"
 + "," + "The next day is:" + year + "March 1st of the year");
 else {
 if (day == 28)
 System.out.println("The date you entered is:" + year + "Year" + month
 + "month" + day + "day" + "n" + "And the previous day is:" + year
 + "February 27th of the year" + "," + "The next day is:" + year + "February 29, year");
 else
 System.out.println("The date you entered is illegal");
 }
 }
 } else
 System.out.println("The date you entered is illegal" );
 }
}