assignment 1

package q1;
import javax.swing.*;
public class Q1
{
    public static void main (String[] args)
    {
        int day,month,year;
        String input = JOptionPane.showInputDialog("Enter date (mm/dd/yyyy)");//input prompt
        String text = "";
        if (input.length() == 10 && input.substring(2,3).equals("/") && input.substring(5,6).equals("/"))//format check
        {
            month = Integer.parseInt(input.substring(0,2));//convert to int
            day = Integer.parseInt(input.substring(3,5));
            year = Integer.parseInt(input.substring(6,10));

            if (year >= 1000 && year < 10000)//year has 4 characters
            {
                if (month == 2)
                    //leap year february check
                {
                    if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
                      //leap year verification

                    {
                        if (day < 1 || day > 29)
                            //leap years has 29 days in february
                        {
                            text= "The day of leap year inputed: "+day+" is invalid, should between 1 to 29";

                        }
                        else
                        {
                             text= "The Date inputed: "+input+" is valid.";
                        }
                    }
                    else
                    {
                        if (day < 1 || day > 28)
                            //non leap years have 28 days february
                        {
                            text= "The day of not leap year inputed: "+day+" is invalid, should between 1 to 28";

                        }
                        else
                        {
                             text= "The Date inputed: "+input+" is valid.";
                        }
                    }
                }
                else if (month > 0 && month < 13 && month != 2)
                {
                    if (month==4||month==6||month==9||month==11)
                    {
                        if (day < 1 || day > 30)
                        {
                            text= "The day of month inputed: "+day+" should not larger than 30, the month of "+month+" only have 30 days";

                        }
                        else
                        {
                             text= "The Date inputed: "+input+" is valid.";
                        }
                    }
                    else
                    {
                        if (day < 1 || day > 31)
                        {
                            text= "The day of month inputed: "+day+" should not larger than 31";

                        }
                        else
                        {
                             text= "The Date inputed: "+input+" is valid.";
                        }
                    }
                }
                else
                {
                    text= "The month inputed: "+month+" is invalid, should between 1 to 12";

                }
            }
            else
            {
                text= "Invalid year value "+year+"";

            }
        }
        else
        {
            text= "Invalid Date format "+input+" eg: 12/31/2018";

        }
         JOptionPane.showMessageDialog(null, text);
        System.exit(0);
    }
}