Hello, I am currently working on an assignment that I can not completely finish, I have all but the c step. I will post the assignment then what I have, how can I : Incrementing into the next month in a leap year, for example, use date: 02/28/2012  STEP 2: Date (20 points)

Create a program called Date.java to perform
error-checking on the initial values, for instance: fields month, day, and year.
Also, provide a method nextDay() to increment the day by one. The Date object
should always remain in a consistent state.

Write a program called DateTest.java that
prompts the user to enter the month, day, and year as numeric values. This
program then creates a Date object using the Date class you just created and
tests the nextDay() method. This can be done in a loop of 40 iterations: the
Date object calls the nextDay() method and prints the date during each iteration
of the loop. This loop is to illustrate that the nextDay() method works
correctly. Test the following cases:

1. Incrementing into the next month, for example, use date:
   02/28/2011
2. Incrementing into the next year, for example, use date:
   11/27/2011
3. Incrementing into the next month in a leap year, for example,
   use date: 02/28/2012

This is what I have so far:

package datePackage;

public class Date

{

    private int year;

    private int month;

    private int day;

    // constructor

    public Date(int year, int month, int day)

    {

        this.year = year;

        this.month = month;

        this.day = day;    

        if (month < 1 || month > 12)

            throw new
IllegalArgumentException("Invalid Month");

        if (!validDay())

            throw new
IllegalArgumentException("Invalid Day");

    }

    // move to next day

    public void nextDay()

    {

        day++;

        if (!validDay())

        {

            System.out.println("Day "
+ day + " invalid. Set to day 1.");

            day = 1;

            if (++month == 13)

            {

                month = 1;

                year++;

            }

        }

    }

    // check valid

    public boolean validDay()

    {

        int[] monthDay = {31, 28, 31, 30, 31,
30, 31, 31, 30, 31, 30, 31};

        boolean leap = (year % 400 == 0) ||
(year % 4 == 0 && year % 100 != 0);

        int addDay = (month == 2 &&
leap) ? 1 : 0;

        if (month >= 1 && month
<= 12 && day > 0 && day <= monthDay[month - 1] +
addDay)

            return true;

        return false;

    }

    // accessors

    public int getYear()

    {

        return year;

    }

    public int getMonth()

    {

        return month;

    }

    public int getDay()

    {

        return day;

    }   

}

 package datePackage;

public class DateTest

{

    // the main method

    public static void main(String[] args)

    {

        System.out.println("Checking
increment");

        Date dat = new Date(2010, 11, 21);

        System.out.println("Date object
constructor for date " + dat.getMonth() + "/" +

                dat.getDay() + "/" +
dat.getYear());

        for (int i = 0; i < 100; i++)

        {

            dat.nextDay();

System.out.println("Incremented Date: " + dat.getMonth() +
"/" +

                    dat.getDay() +
"/" + dat.getYear());

        }

    }

}