我在做一些事情上遇到了困难。我是Java的新手，由于八进制数字，我无法弄清楚如何读取前两位数来确定08或09。此外，我得到一个返回null，1,199，不需要在那里。帮助将不胜感激。
import java.util.*;
public class Dates {
public static void main(String[] args) {
String January,February, March, April, May, June, July,
August, September,October, November, December, month;
January = February = March = April = May = June = July =
August = September = October = November = December = month = null;
Scanner myScanner = new Scanner(System.in);
System.out.print("Enter date in the format mm/dd/yyyy: ");
String input = myScanner.next();
String months = input.substring(0,1);
int monthInt = Integer.parseInt(months);
if (monthInt == 01){
month = January;
}
else if (monthInt == 02){
month = February;
}
else if (monthInt == 03){
month = March;
}
else if (monthInt == 04){
month = April;
}
else if (monthInt == 05){
month = May;
}
else if (monthInt == 06){
month = June;
}
else if (monthInt == 07){
month = July;
}
else if (monthDouble == 08){
month = August;
}
else if (monthDouble == 09){
month = September;
}
else if (monthInt == 10){
month = October;
}
else if (monthInt == 11){
month = November;
}
else if (monthInt == 12){
month = December;
}
else {
System.out.println("Invalid Month");
}
String days = input.substring(3,4);
int daysInt = Integer.parseInt(days);
if ((daysInt <= 31) && (monthInt == 1 || monthInt == 3 || monthInt ==
5 || monthInt == 7 || monthInt == 8 || monthInt == 10 || monthInt
== 12)){
daysInt = daysInt;
}
else if ((daysInt <= 30) && (monthInt == 4 || monthInt == 6 || monthInt
== 9 || monthInt == 11)){
daysInt = daysInt;
}
else if ((daysInt <= 28) && (monthInt == 2)){
daysInt = daysInt;
}
else
System.out.println("Invalid Day");
String year = input.substring(6,9);
int yearInt = Integer.parseInt(year);
if (yearInt >= 1900 && yearInt <= 2014) {
yearInt = yearInt;
}
else {
System.out.println("Year should be between 1900 and 2014");
}
String checkSlash = input.substring(2);
char slash = checkSlash.charAt(0);
if (slash == '/')
slash = slash;
else
System.out.println("Invalid format. Use mm/dd/yyyy");
System.out.println(month + " " + daysInt + ", " + year);
}
}
答案 0 :(得分：4)
有更好的方法可以做到这一点，最明显的是使用Java的Date和SimpleDateFormat类，但是如果你必须知道......
不要在整数上包含前导零。你不会是reading or otherwise dealing with八进制值。 1月是第一个月，将其表示为1更为直接。
如果你真的不想使用SimpleDateFormat，我会给你一个替代方案。考虑到我们知道所有值都落在一个整数范围内（也就是说，它们都将小于21亿）。如果我们让Integer类为我们解析值，那么我们可以用更少的代码来完成。
除此之外，我们不需要担心奇怪的子串（顺便说一句，你的只会抓住第一个元素 - 这是有问题的。）
让我们使用String#split()方法并在正斜杠上分解输入字符串。
String[] brokenInput = input.split("/");
现在，根据我们的格式和惯例，我们会看到月份位于brokenInput[0]，brokenInput[1]中的日期和brokenInput[2]中的年份。
解析很容易：
Integer monthInt = Integer.parseInt(brokenInput[0]);
Integer daysInt = Integer.parseInt(brokenInput[1]);
Integer yearInt = Integer.parseInt(brokenInput[2]);
答案 1 :(得分：2)
尝试更简单的方法
String strDate = "11/29/2009";
SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy");
Date dateStr = formatter.parse(strDate);
答案 2 :(得分：1)
Java会将前导零的数字视为 octals ，八进制数中的数字不能大于7.如果您尝试使用08，{{{ 1}}。您可以改为使用09：
String我认为（因为你要与“01”，“02”，...）进行比较，你应该使用if (months.equals("01"))
...
：
substring(0,2)答案 3 :(得分：0)
我会假设你有很长的路要走。
首先，在检查月份时删除0值的前导int，他们会将值转换为八进制，这是您不需要的...
if (monthInt == 1) {
month = January;
} else if (monthInt == 2) {
month = February;
} else if (monthInt == 3) {
month = March;
} else if (monthInt == 4) {
month = April;
} else if (monthInt == 5) {
month = May;
} else if (monthInt == 6) {
month = June;
} else if (monthInt == 7) {
month = July;
} else if (monthInt == 8) {
month = August;
} else if (monthInt == 9) {
month = September;
} else if (monthInt == 10) {
month = October;
} else if (monthInt == 11) {
month = November;
} else if (monthInt == 12) {
month = December;
} else {
System.out.println("Invalid Month");
}
此...
String months = input.substring(0, 1);
将获得输入的第一个字符，但您已向用户询问mm/dd/yyyy，这表示您想要一个月和日的两位数值...此外，如果他们输入会发生什么在12？
相反，您可以使用String[] parts = input.split("/");在input分隔符上拆分String /，这（如果输入有效）将为您提供三个元素，每个元素各一个部分日期值。
然后你可以使用......
int monthInt = Integer.parseInt(parts[0]);
//...
int daysInt = Integer.parseInt(parts[1]);
//...
int yearInt = Integer.parseInt(parts[2]);
转换单个元素。
这就提出了一个问题，即在尝试拆分之前，你应该以一种有意义的方式验证输入值。
月份值均为null
String January, February, March, April, May, June, July,
August, September, October, November, December, month;
January = February = March = April = May = June = July
= August = September = October = November = December = month = null;
这基本上意味着您的输出始终以null开头。你实际上需要为这些分配一些有意义的价值。
我也会嘲笑其他人所说的话，除非你有充分的理由不这样做，我会用Calendar和某种DateFormat来做这一切。 ..
更新了（略高于顶部）示例
这基本上理解了您的想法并使用SimpleDateFormat和Calendar来执行输入的实际检查，例如......
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Scanner;
public class Dates {
public static void main(String[] args) {
Scanner kb = new Scanner(System.in);
System.out.println("Date (mm/dd/yyyy):");
String input = kb.nextLine();
// This is a little excessive, but does a pre-check of the basic
// format of the date. It checks for a strict adhereance to
// the nn/nn/nnnn format. This might not be required as
// SimpleDateFormat can actually be configured to be lient in it's
// parsing of values
if (input.matches("[0-9]{2}/[0-9]{2}/[0-9]{4}")) {
try {
// Parse the String input to a Date object
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
Date date = sdf.parse(input);
// Create a Calendar, going to use this to compare the resulting
// Date value, as the parser will auto correct the input
Calendar cal = Calendar.getInstance();
cal.setTime(date);
// Split the basic input along the / delimeter
String parts[] = input.split("/");
boolean valid = true;
// Check each part to make sure it matches the components of the date
if (Integer.parseInt(parts[0]) != cal.get(Calendar.MONTH) + 1) {
valid = false;
System.out.println(parts[0] + " is not a valid month");
}
if (Integer.parseInt(parts[1]) != cal.get(Calendar.DATE)) {
valid = false;
System.out.println(parts[1] + " is not a valid day of the month");
}
if (Integer.parseInt(parts[2]) != cal.get(Calendar.YEAR)) {
valid = false;
System.out.println(parts[2] + " is not a valid year");
}
if (valid) {
// Print the result...
System.out.println(new SimpleDateFormat("MMMM dd, yyyy").format(date));
}
} catch (ParseException ex) {
System.out.println("Unable to parse " + input + "; invalid format");
}
} else {
System.out.println("Invalid format");
}
}
}