HELP, date class and parsing input

Question

I have reviewed many posts in these forums and have found that detail gets the best results so I apologize in advance if this is detailed. I am taking a Java class and am not doing so hot. The last time I programmed was in 1998 and that was Ada, I very soon moved to Networking. I guess those that can't program become networkers, I don't know, but I am frustrated here.
Any how I am trying to write a rather simple program, but it is the manipulation of the date I am having difficulty with. Here are the requirements:
Overall Requirements
Create a class named Date that stores date values and prints out the date in either a pure numeric format or a name and number format (see sample session for format details).
Date.java class file
? Date objects should store the date in two int instance variables ─ day and month, and it should include the String instance variable, error, initialized with null.
Implement a 1-parameter Date constructor that receives a dateStr string parameter and performs complete error checking on the given dateStr value. The Date constructor is the entity that?s responsible for date error checking. That way, if a Date object is instantiated and if there are no errors, then you?re guaranteed that the Date object holds a legitimate date value. If any kind of error occurs, change the value of the error instance variable to a non-null string value, using an appropriate concatenation of a string constant, input substring, and/or API exception message.
Constructors use the same exception handling rules as methods: In a try block, include the parsing of the month and day substrings and other error-checking logic that will not work if parsing fails.
? Take into account the actual number of days in each month, but assume that there are always 28 days in February.
? To extract day and month numbers from the given date string, use String?s indexOf method to find the location of the slash character, and String?s substring method to extract month and day substrings from the input string.
? Include a method for printing the date with a numeric format. Use the zero-pad flag in a printf method call to get exactly two digits for each month and day.
? Include a method for printing the date with an alphabetic format.
Include a getError method which returns the value of the error instance variable.
DateDriver.java class file : In your driver class, include a loop that repeatedly:
? Asks the user to enter a date or ?q? to quit. ? If the entry is not ?q?, instantiate a Date object.
? If the error variable is null: o Print the date using numeric format.o Print the date using alphabetic format. Otherwise, print the value of the error variable.
I want to figure this out on my own as much as possible but have until tomorrow night to do so..............I need to understand how I can use Strings indexOf to parse the dateStr so I can locate the /. I see I can use it to find the position of a specified character, but I am not sure of the syntax I need to use. But then once I find the / I need to use the String's substring method to extract month and day. I think I might be able to get that, if I can get the / figured out.
The below is what I have in my Class and my Driver so far:
*DateDriver.java (driver program)
* Christine Miller-Lane
*Overall Requirements
*Create a class named Date that stores date values and prints out the date in either a pure numeric
format or a name and number
*format (see sample session for format details).
*DateDriver.java class file
*In your driver class,
*????????? If the error variable is null:
*     ◦     Otherwise, print the value of the error variable.
import java.util.*;
public class DateDriver
Date datevalue;
public static void main(String[] args)
     Scanner stdIn = new Scanner(System.in);
     while (!xStr.equalsIgnoreCase("q"))
     try
          System.out.println("Enter a date in the form mm/dd ("q" to quit): ";
          value = stdIn.nextLine();
          datevalue = new Date(value);                                                        //instaniate the date object
          System.out.println //print date in numeric format
          System.out.println //print date in alphabetic format
          break;
          catch
          System.out.println("print value of error variable.");
          stdIn.next(); // Invalid input is still in the buffer so flush it.
     } //endloop
     }//end main
} //end class?
* Date.java
* Christine Miller-Lane
*Overall Requirements
*Create a class named Date that stores date values and prints out the date in either a pure numeric format or a name
*and number format (see sample session for format details).
*Date.java class file
*????????? Date objects should store the date in two int instance variables ─ day and month, and it should include
*the String instance variable, error, initialized with null.
*     ?     Implement a 1-parameter Date constructor that receives a dateStr string parameter and performs complete
*     error checking on the given dateStr value. The Date constructor is the entity that?s responsible for date error
*     checking. That way, if a Date object is instantiated and if there are no errors, then you?re guaranteed that the
*     Date object holds a legitimate date value. If any kind of error occurs, change the value of the error instance
*     variable to a non-null string value, using an appropriate concatenation of a string constant, input substring,
*     and/or API exception message.?
*     ?     Constructors use the same exception handling rules as methods: In a try block, include the parsing of the
*     month and day substrings and other error-checking logic that will not work if parsing fails.
*????????? Take into account the actual number of days in each month, but assume that there are always 28 days in February.
*????????? To extract day and month numbers from the given date string, use String?s indexOf method to find the
*location of the slash character, and String?s substring method to extract month and day substrings from the input string.
import java.util.*;
public class Date
     Scanner stdIn = new Scanner(System.in);
     boolean valid = false
     int day;
     int month;
     String error = null;
     String dayStr;
     String monthStr;
     String dateStr;
     public Date(String dateStr)
// Look for the slash and set appropriate error if one isn't found. use String?s indexOf method to find the
//location of the slash character and String?s substring method to extract month and day substrings from the input string.
// Convert month portion to integer. Catch exceptions and set appropriate error if there are any.
Integer.parseInt(dateStr);
// Validate month is in range and set appropriate error if it isn't.
// Convert day portion to integer. Catch exceptions and set appropriate error if there are any.
// Validate day is in range based on the month (different days per month) and set appropriate error if it isn't.
//public void printDate()      //Include a method for printing the date with a numeric format. Use the zero-pad flag in a printf method
                                   //call to get exactly two digits for each month and day.
//{                                   //Include a method for printing the date with an alphabetic format.      
//     } // end print report
//     public getError()
                              //Include a getError method which returns the value of the error instance variable.
}//end class Date
Here is sample out put needed::::::::
Sample Session:
Enter a date in the form mm/dd ("q" to quit): 5/2
05/02
May 2
Enter a date in the form mm/dd ("q" to quit): 05/02
05/02
May 2
Enter a date in the form mm/dd ("q" to quit): 52
Invalid date format ? 52
Enter a date in the form mm/dd ("q" to quit): 5.0/2
Invalid format - For input string: "5.0"
Enter a date in the form mm/dd ("q" to quit): 13/2
Invalid month ? 13
Enter a date in the form mm/dd ("q" to quit): 2/x
Invalid format - For input string: "x"
Enter a date in the form mm/dd ("q" to quit): 2/30
Invalid day ? 30
Enter a date in the form mm/dd ("q" to quit): 2/28
02/28
February 28
Enter a date in the form mm/dd ("q" to quit): q
I am trying to attack this ONE STEP at a time, even though I only have until Sunday at midnight. I will leave this post and get some rest, then attack it again in the morning.
Edited by: stillTrying on Jul 12, 2008 8:33 PM

Answer 1

Christine,
You'r doing well so far... I like your "top down" approach. Rough out the classes, define ALL the methods, especially the public one... but just sketch out the requirements and/or implementation with a few comments. You'll do well.
(IMHO) The specified design is pretty crappy, especially the Exception handling
[The Constructor] performs complete error checking on the given dateStr value. The Date constructor is the entity that?s responsible for date error checking. That way, if a Date object is instantiated and if there are no errors, then you?re guaranteed that the Date object holds a legitimate date value. If any kind of error occurs, change the value of the error instance variable to a non-null string value, using an appropriate concatenation of a string constant, input substring, and/or API exception message.Please allow me to shred this hubris piece by piece.
[The Constructor] performs complete error checking on the given dateStr value. The Date constructor is the entity that?s responsible for date error checking.Umm... Well I suppose it could... but NO, the constructor should delegate such "complex validation" to a dedicated validate (or maybe isValid) method... which might even be made publicly available... it's a good design.
That way, if a Date object is instantiated and if there are no errors, then you?re guaranteed that the Date object holds a legitimate date value. If any kind of error occurs, change the value of the error instance variable to a non-null string value ...Utter Bollocks! When passed an invalid input string the, Date constructor should throw an InvalidDataException (or similar). It should not SILENTLY set some dodgy error errorMessage attribute, which is returned later by a "print" method. We tried that in masm, fortran, ada, basic, c, and pascal for twenty odd years. It sucked eggs. And it STILL sucks eggs. Java has a "proper" try/catch exception handling mechanism. Use it.
I mean, think it through...
  someDate = get a date from the user // user enters invalid date, so someDate is null and errMsg is set.
  report = generateReport() // takes (for the sake of argument) three hours.
  emailReport(someDate, report) // only to fail at the last hurdle with an InvalidDataException!And anyways... such implementation details are traditionally the implementors choice... ie: it's usually between the programmer and there tech-manager (if they're lucky enough to have one).
Cheers. Keith.