How to do a date validation with leap years

Question

I'm doing a date validation program in my Java class, and well it's pretty hard (for me that is). I have to be able to type in a date, have it say whether it's a leap year or not, and print out the number of days in the month. It seems pretty straight forward, but I get confused on trying to do the 'if else' statements and even the simplest things like getting the day prompting to work. >< The years I'm doing only goes through 1000 to 1999, so that's why those numbers are there. The program isn't complete, so if anyone could help show me what I'm doing wrong in the areas I'm working on then I'd appreciate it...and I'm still kind of in the basics of Java so if you do hint me with some code then I'd appreciate it if it was stuff that's not too advanced so yea.
// Dates.java
// Determine whether a 2nd-millenium date entered by the user
// is valid
import java.util.Scanner;
public class Dates
public static void main(String[] args)
int month, day, year; //date read in from user
int daysInMonth; //number of days in month read in
boolean monthValid, yearValid, dayValid; //true if input from user is valid
boolean leapYear; //true if user's year is a leap year
Scanner scan = new Scanner(System.in);
//Get integer month, day, and year from user
System.out.print("Type in the month: " );
          month = scan.nextInt();
System.out.print("Type in the day: " );
          day = scan.nextInt();
System.out.print("Type in the year: " );
          year = scan.nextInt();
//Check to see if month is valid
if (month >= 1)
month = month;
else
if (month <= 12)
month = month;
else;
//Check to see if year is valid
if (year >= 1000)
year = year;
else
if (year <= 1999)
year = year;
else;
//Determine whether it's a leap year
//Determine number of days in month
if (year == 1 || 3 || 5 || 7 || 8 || 10 || 12)
     System.out.println (Number of days in month is 31);
     else (year == 4 || 6 || 9 || 11)
     System.out.println (Number of days in month is 30);
//User number of days in month to check to see if day is valid
//Determine whether date is valid and print appropriate message
// Dates.java
// Determine whether a 2nd-millenium date entered by the user
// is valid
import java.util.Scanner;
public class Dates
public static void main(String[] args)
int month, day, year; //date read in from user
int daysInMonth; //number of days in month read in
boolean monthValid, yearValid, dayValid; //true if input from user is valid
boolean leapYear; //true if user's year is a leap year
Scanner scan = new Scanner(System.in);
//Get integer month, day, and year from user
System.out.print("Type in the month: " );
          month = scan.nextInt();
System.out.print("Type in the day: " );
          day = scan.nextInt();
System.out.print("Type in the year: " );
          year = scan.nextInt();
//Check to see if month is valid
if (month >= 1)
month = month;
else
if (month <= 12)
month = month;
else;
//Check to see if year is valid
if (year >= 1000)
year = year;
else
if (year <= 1999)
year = year;
else;
//Determine whether it's a leap year
//Determine number of days in month
if (year == 1 || 3 || 5 || 7 || 8 || 10 || 12)
     System.out.println (Number of days in month is 31);
     else (year == 4 || 6 || 9 || 11)
     System.out.println (Number of days in month is 30);
//User number of days in month to check to see if day is valid
//Determine whether date is valid and print appropriate message
}

Answer 1

Here are some helpfull hints for you:
1. Your code is really hard to read, there are two main reasons for this. First, your indentation sucks. Second, you seem to be fascinated with saving two (ok four if you count the shift key) keypresses to avoid using { and }.
2. Not using the brackets (you know { and } which you like to avoid) also is causing your code to do some stuff you don't realize or want to happen, or at least it would be if your code compiled.
3. If statements require arguements, "year == 1" is an arguement, "3" is not an arguement. Each operator like the or operator ("||") is essentially a new if and requires a complete arguement. So the following code peice:
if (year == 1 || 3 || 5 || 7 || 8 || 10 || 12)Literally translates to if year equals 1 or if 3 or if 5 or if 7 or if 8 or if 10 or if 12. Doesn't make much sense in english, and it doesn't make much sense in Java either.
4. I am pretty sure "year" is not the variable you want in the code snippet above (the one used in hint 3), especially considering years 1, 3, 5, 7, 8, 10, and 12 are not between 1000 and 1999. You need to be really carefull not make these kind of mistakes when coding, because they are by far the hardest to track down and fix later since they don't really throw up any flags or anything at compile or run time. Take your time and think thuroughly about each line of code while coding it, it will save you tons of time in the long run.
5. What exactly do you expect statements like "month = month;" to do? That translates as make month equal to month. Do you go to the bank and say " I have exactly $3.56 in my pocket, so I would like to deposite all $3.56 and then withdraw $3.56 and put it back in my pocket"? How do you think the teller would look at you? Teller would probably do it, but the teller would feel like he/she wasted time with you and that you are not really right in the head. Java feels the same way when you make it do the same thing, and you love to do it.
6. Code like the following is all wrong, and for more reasons than pointed out in hint 5.
if (month >= 1)
month = month;
else
if (month <= 12)
month = month;
else;Let's say someone put 13 in as the month. It passes the first check because 13 is greater than or equal to 1. so month which is 13, now gets set to 13 (gee that was effective). Now we hit the else and things get confusing because you didn't use brackets or proper indentation (hint 1) so we don't know what your real intent was. Did you mean else do nothing, and the next if statement is then executed, or did you mean to just run the next if statement if the else condition was met? Fortunatly it doesn't matter here because the next if statement is failed anyways since 13 is not less than or equal to 12.
So, we leave this code with month ebing 13, wait when did we add a 13th month to the calendar? Are you using the Jewish calendar? Could be, except even if I put 1234567 as the month your code would except it as valid, and I know no calendar with that many months. Try writing this in english first and translating it to jave, like i would probably say "if the month is greater than or equal to 1 and less than or equal to 12 then the month is valid." Course now what do you do if it is invalid? Hmm, maybe I would actually say "while the month is less than 1 or greater than 12 ask the user for the month" until they get it right.
There are a few other problems, but most of them are probably things you haven't learned yet, and they are not show stoppers so we will let them fly. You already have a lot of work to do to make this better. But I do have one more really really big usefull hint for you:
Never, ever, under any circumstances, should you ever ask in any way or even hint at asking for someone else to provide code solutions to your problems. So "so if you do hint me with some code then I'd appreciate it if it was stuff that's not too advanced " was a very bad thing to do, but fortunatly for you you followed it with proof you were trying to write the code yourself. Had the code you provided not been so full of problems it was obvious a beginner wrote it, you would probably have gotten much less cordial responses. I would seriously consider avoiding any implication of wanting code, at least until you become a regular poster here and people know you are not just looking to get your homework done for you.
Hope some of this helps.
JSG