java编程 输出昨天日期

Question

设计一个函数，该函数功能为：根据入口参数Today，函数返回Today的前一天Yesterday， 入口参数Today和出口参数Yesterday均为8位定长的字符串，格式为：YYYYMMDD。例如：Today=”20040303”，函数返回Yesterday为：”20040302”； Today=”20040301”，函数返回Yesterday为：”20040229”。
为简单，不需要对Today的格式做合法性检查。
C语法定义为，int getYesterday ( char * Today , char * Yesterday ) ；
Java 语法定义为，static String getYesterday ( String Today )，返回值为Yesterday;
注：可能用到的字符串转化为整数的参考函数有int atoi( char * )，static int Integer.parseInt( String )；如果使用Java编程，只允许使用字符串类String等基本的方法和类，不允许使用java某些特有类以及这些类自带的方法，如java.util.Date类、java.util.Calendar类。

Answer 1

public class DateCalcu {
public static String getYesterday(String Today) {
String Yes = "";
String year = "", month = "", day = "";
int y = 0, m = 0, d = 0;
year = Today.substring(0, 4);
month = Today.substring(4, 6);
day = Today.substring(6, 8);
y = Integer.parseInt(year);
m = Integer.parseInt(month);
d = Integer.parseInt(day);
d = d - 1;
if (d == 0) {
m = m - 1;
if (m == 1 || m == 3 || m == 5 || m == 7 || m == 8 || m == 10) {
d = 31;
}
if (m == 2)
if ((y % 4 == 0 && y % 100 != 0) || (y % 400 == 0)) // 如果是闰年
d = 29;
else
d = 28;
else if (m != 0)
d = 30;
}
if (m == 0) {
y = y - 1;
m = 12;
d = 31;
}
year = String.valueOf(y);
if (m < 10)
month = "0" + String.valueOf(m);
else
month = String.valueOf(m);
if (d < 10)
day = "0" + String.valueOf(d);
else
day = String.valueOf(d);
Yes = year + month + day;

return Yes;
}

public static void main(String args[]) {
String yesterday = "20090301";
System.out.println("今天是" + yesterday);
yesterday = getYesterday(yesterday);
System.out.println("昨天是" + yesterday);
}
}
////////
//看看符合不符合你的要求

Answer 2

public class AA {

public static String getYesterday(String today){
String yearStr = today.substring(0, 4);
String monthStr = today.substring(4,6);
String dateStr = today.substring(6);

int year = Integer.parseInt(yearStr);
int month = Integer.parseInt(monthStr);
int date = Integer.parseInt(dateStr);

String yesterday = null;

if(date > 1 && date < 11){
yesterday = yearStr + monthStr + "0" + String.valueOf(date - 1);
}else if(date >= 11){
yesterday = yearStr + monthStr + String.valueOf(date - 1);
}
if(date == 1){
if(month == 5 || month == 7 || month == 10){
yesterday = yearStr + "0" + String.valueOf(month - 1) + "30";
}else if(month == 12){
yesterday = yearStr + String.valueOf(month - 1) + "30";
}else if(month == 11){
yesterday = yearStr + String.valueOf(month - 1) + "31";
}else if(month == 3){
if(year % 4 == 0 && year % 100 != 0 || year % 400 == 0){
yesterday = yearStr + "0229";
}else{
yesterday = yearStr + "0228";
}
}else if(month == 1){
yesterday = String.valueOf(year - 1) + "1231";
}else{
yesterday = yearStr + "0" + String.valueOf(month - 1) + "31";
}
}

return yesterday;
}

public static void main(String[] args) {
String s1 = AA.getYesterday("20070305");//date > 1 && date < 11
String s2 = AA.getYesterday("20070311");//date >= 11
//以下date == 1
String s3 = AA.getYesterday("20071001");//month == 5 || month == 7 || month == 10
String s4 = AA.getYesterday("20071201");//month == 12
String s5 = AA.getYesterday("20071101");//month == 11
String s6 = AA.getYesterday("19040301");//month == 3闰年
String s7 = AA.getYesterday("19000301");//month == 3非闰年
String s8 = AA.getYesterday("20070101");//month == 1
String s9 = AA.getYesterday("20070201");//month == 2
System.out.println(s1);
System.out.println(s2);
System.out.println(s3);
System.out.println(s4);
System.out.println(s5);
System.out.println(s6);
System.out.println(s7);
System.out.println(s8);
System.out.println(s9);
}
}

Answer 3

这题没什么意义