learning how to use classes

[Joseph Swager]

Hello all. Hope this isnt a dumb question. I'm writing code to compare two dates and list the difference in months between dates.
works for the year but i keep getting the same answer for the months. example june 1980 and then the date to compare it to may 1982

the answer will be 23 months. but my code would return 24.
then if i enter the same for the first date then January 1984 then it would be 42 but mine will return 48

I commented where i think i went wrong but if anyone can tell me where i went wrong please let me know. its driving me crazy.

 
import java.util.Scanner;

public class DateCompare {

	private String month; 
    private int day;
    private int year; //a four digit number.

    public void writeOutput( )
    {
        System.out.println(month + " " + day + ", " + year); 
    }

    public void readInput( )
    {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enter month, day, and year.");
        System.out.println("Do not use a comma.");
        month = keyboard.next( );
        day = keyboard.nextInt( );
        year = keyboard.nextInt( );
    }

    public int getDay( )
    {
        return day;
    }

    public int getYear( )
    {
        return year;
    }
    
    public int getMonth( )
    {
        return getMonth(month);
    }
    
    public int getMonth(String mon )
    {
        if (month.equalsIgnoreCase("January"))
            return 1;
        else if (month.equalsIgnoreCase("February"))
            return 2;
        else if (month.equalsIgnoreCase("March"))
            return 3;
        else if (month.equalsIgnoreCase("April"))
            return 4;
        else if (month.equalsIgnoreCase("May"))
            return 5;
        else if (month.equals("June"))
            return 6;
        else if (month.equalsIgnoreCase("July"))
            return 7;
        else if (month.equalsIgnoreCase("August"))
            return 8;
        else if (month.equalsIgnoreCase("September"))
            return 9;
        else if (month.equalsIgnoreCase("October"))
            return 10;
        else if (month.equalsIgnoreCase("November"))
            return 11;
        else if (month.equalsIgnoreCase("December"))
            return 12;
        else
        {
            System.out.println("Fatal Error");
            System.exit(0);
            return 0; //Needed to keep the compiler happy
        }
    }
    
    public  int  monthsUntil(String monthToCompare, int yearToCompare)
    {
    	int theMonth = getMonth(monthToCompare); // this doesnt work returns the same as what d1 is
    	int theYear = yearToCompare;
    	int yearCompaired = getYear();
    	int monthCompaired = getMonth();
    	
    	   	
    	int diff = ((monthCompaired - theMonth) - ((yearCompaired - theYear) * 12));
    	
    	if (diff > 0)
    		return diff;
    	else if (diff < 0)
    		return diff * -1;
    	else
    		return 0;
    }
	
	public static void main(String[] args) {
		Scanner keyboard = new Scanner(System.in);
		
		DateCompare d1 = new DateCompare();
		d1.readInput();
		
		int newYear;
		String newMonth;
		int theDiff;
		
		System.out.println("Enter a month and year to compare: ");
		newMonth = keyboard.next();
		newYear = keyboard.nextInt();
		
		theDiff = d1.monthsUntil(newMonth,newYear);
		
		System.out.println("The diffrence in months is " + theDiff);
		
		
	}//end main

}// end class

   

[Pushkar Choudhary]

Just scanning through the code, I could spot one potential problem: In the getMonth() method, you are taking String "mon" as an argument, but then you are not using it anywhere in the method, instead you are comparing the class-level "month" variable value with String month names. So, the value "newMonth" obtained in the main method is getting lost in the process, since the months you compare are always the same (i.e. both are values got from class level variable "month"). This is probably the reason why your code only finds difference in the years entered, and then multiplies it by 12 and gives the answer in number of months and you are getting answers like 12 months, 24 months, 48 months etc.

Other than this, in the monthsUtil method, I find the logic to calculate the "diff" a bit weird. For example, if you choose January 2000 and June 2001 as your two dates, then the expression

int diff = ((monthCompaired - theMonth) - ((yearCompaired - theYear) * 12));

would give the answer as 7, which is incorrect. I guess you would need to work on this logic a bit.

[Pushkar Choudhary]

Another question is why are you asking for the "day" only once? If you want to compare the dates by considering the day-of-month, then you should also ask for the day value to be compared. Then you would also need to modify the logic for calculating the "diff" (mentioned in my previous reply) by considering the day along with the month and the year values.

[Pushkar Choudhary]

Oh, and Welcome to Javaranch!

[Joseph Swager]

Thank you so far for the answers. Oh and i got rid of day from the program. sorry for the confusion.
Everything works the way i want it but when i need to do the diffrence math on the month.

 tScanner keyboard = new Scanner(System.in);
		
		DateCompare d1 = new DateCompare();
		d1.readInput();
		
		int newYear;
		String newMonth;
		int theDiff;
		
		System.out.println("Enter a month and year to compare: ");
		newMonth = keyboard.next();
		newYear = keyboard.nextInt();
		
		theDiff = d1.monthsUntil(newMonth,newYear);
		

so lets say when i'm promted for d1 info and i enter June 1980

and now im entering info to compare so i enter July 1981

now the diff should be 13 but its coming back 12.


im passing in the new dates to a method and using it to d1 with

   theDiff = d1.monthsUntil(newMonth,newYear); 

   public  int  monthsUntil(String monthToCompare, int yearToCompare)
    {
    	int theMonth = this.getMonth(monthToCompare); 
    	int theYear = yearToCompare;
    	int yearCompaired = getYear();
    	int monthCompaired = getMonth();
    	
    	   	
    	int diff = ((monthCompaired - theMonth) - ((yearCompaired - theYear) * 12));
    	
    	if (diff > 0)
    		return diff;
    	else if (diff < 0)
    		return diff * -1;
    	else
    		return 0;
    }  

only problem i am having is theMonth and the month always seem to have the same value. Its like the newMonth value im passing is getting d1 value no matter what.

I just want to know why this wouldnt work

[Joseph Swager]

Yeah i see the logic problem thank you.

[Joseph Swager]

Hey Pushkar Choudhary,
You where right on the math i changed the - to + and it works

also i was forgetting to add a string var in getMonth ( string month) method. here is the final code and it works like i wanted. thank you thank you.
I'm loving to learn Java.

import java.util.Scanner;

public class DateCompare {

	private String month; 
    private int year; //a four digit number.

    public void writeOutput( )
    {
        System.out.println(month + " "  + year); 
    }

    public void readInput( )
    {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enter month, day, and year.");
        System.out.println("Do not use a comma.");
        month = keyboard.next( );
        year = keyboard.nextInt( );
    }

    public int getYear( )
    {
        return year;
    }
    
    public int getMonth( )
    {
        return getMonth(month);
    }
    
    public int getMonth(String mon )
    {
    	String month = mon;
        if (month.equalsIgnoreCase("January"))
            return 1;
        else if (month.equalsIgnoreCase("February"))
            return 2;
        else if (month.equalsIgnoreCase("March"))
            return 3;
        else if (month.equalsIgnoreCase("April"))
            return 4;
        else if (month.equalsIgnoreCase("May"))
            return 5;
        else if (month.equals("June"))
            return 6;
        else if (month.equalsIgnoreCase("July"))
            return 7;
        else if (month.equalsIgnoreCase("August"))
            return 8;
        else if (month.equalsIgnoreCase("September"))
            return 9;
        else if (month.equalsIgnoreCase("October"))
            return 10;
        else if (month.equalsIgnoreCase("November"))
            return 11;
        else if (month.equalsIgnoreCase("December"))
            return 12;
        else
        {
            System.out.println("Fatal Error");
            System.exit(0);
            return 0; //Needed to keep the compiler happy
        }
    }
    
    public  int  monthsUntil(String monthToCompare, int yearToCompare)
    {
    	int theMonth = getMonth(monthToCompare); 
    	int theYear = yearToCompare;
    	int yearCompaired = getYear();
    	int monthCompaired = getMonth();
    	
    	   	
    	int diff = ((monthCompaired - theMonth) + ((yearCompaired - theYear) * 12));
    	
    	if (diff > 0)
    		return diff;
    	else if (diff < 0)
    		return diff * -1;
    	else
    		return 0;
    }
	
	public static void main(String[] args) {
		Scanner keyboard = new Scanner(System.in);
		
		DateCompare d1 = new DateCompare();
		d1.readInput();
		
		int newYear;
		String newMonth;
		int theDiff;
		
		System.out.println("Enter a month and year to compare: ");
		newMonth = keyboard.next();
		newYear = keyboard.nextInt();
		
		theDiff = d1.monthsUntil(newMonth,newYear);
		
		System.out.println("The diffrence in months is " + theDiff);
		
		
	}//end main

}// end class