Date.java

/* Date.java */

import java.io.*;

class Date {

    /* Put your private data fields here. */
    private int month, day, year;

    /** Constructs a date with the given month, day and year.   If the date is
     *  not valid, the entire program will halt with an error message.
     *  @param month is a month, numbered in the range 1...12.
     *  @param day is between 1 and the number of days in the given month.
     *  @param year is the year in question, with no digits omitted.
     */
    public Date(int month, int day, int year) {
        if (isValidDate(month, day, year) == true){
            this.month = month;
            this.day = day;
            this.year = year;
        }else {
            System.out.println("invalid date");
            System.exit(0);
        }

    }

    /** Constructs a Date object corresponding to the given string.
     *  @param s should be a string of the form "month/day/year" where month must
     *  be one or two digits, day must be one or two digits, and year must be
     *  between 1 and 4 digits.  If s does not match these requirements or is not
     *  a valid date, the program halts with an error message.
     */
    public Date(String s) {
//        int delimiter1 = s.indexOf("/");
//        int delimiter2 = s.indexOf("/", delimiter1 + 1);
//        String monthString = s.substring(0, delimiter1);
//        String dayString = s.substring(delimiter1 + 1, delimiter2);
//        String yearString = s.substring(delimiter2 + 1);
//        int month = Integer.parseInt(monthString);
//        int day = Integer.parseInt(dayString);
//        int year = Integer.parseInt(yearString);
        String[] elements = s.split("/");
        int m = Integer.parseInt(elements[0]);
        int d = Integer.parseInt(elements[1]);
        int y = Integer.parseInt(elements[2]);
        if(isValidDate(m, d, y) == false){
            System.out.println("invalid date");
            System.exit(0);
        }else{
            this.month = m;
            this.day = d;
            this.year = y;
        }

    }

    /** Checks whether the given year is a leap year.
     *  @return true if and only if the input year is a leap year.
     */
    public static boolean isLeapYear(int year) {
//        boolean x = false;
//        if(year % 4 == 0){
//            x = true;
//            if(year % 100 == 0){
//                if(year % 400 == 0){
//                    x = true;
//                }else x = false;
//            }
//        }
//        return x;
        if(year % 400 == 0) return true;
        if(year % 100 ==0) return false;
        return year % 4 == 0;
    }

    /** Returns the number of days in a given month.
     *  @param month is a month, numbered in the range 1...12.
     *  @param year is the year in question, with no digits omitted.
     *  @return the number of days in the given month.
     */
    public static int daysInMonth(int month, int year) {
        switch (month){
            case 2:
                if(isLeapYear(year) == true){
                    return 29;
                }else return 28;
            case 4:
            case 6:
            case 9:
            case 11:
                return 30;
            default:
                return 31;
        }
    }

    /** Checks whether the given date is valid.
     *  @return true if and only if month/day/year constitute a valid date.
     *
     *  Years prior to A.D. 1 are NOT valid.
     */
    public static boolean isValidDate(int month, int day, int year) {
        boolean x = false;
        if(1 <= month && month <= 12 && year >=1 && 1 <= day && day <= daysInMonth(month, year)){
            x = true;
        }
        return x;
    }

    /** Returns a string representation of this date in the form month/day/year.
     *  The month, day, and year are printed in full as integers; for example,
     *  12/7/2006 or 3/21/407.
     *  @return a String representation of this date.
     */
    public String toString() {
        return month + "/" + day + "/" + year;
    }

    /** Determines whether this Date is before the Date d.
     *  @return true if and only if this Date is before d.
     */
    public boolean isBefore(Date d) {
        boolean x = false;
        if(year < d.year) {
            x = true;
        }else if(year == d.year){
            if(month < d.month){
                x = true;
            }else if(month == d.month){
                if(day < d.day){
                    x = true;
                }
            }
        }
        return x;
    }

    /** Determines whether this Date is after the Date d.
     *  @return true if and only if this Date is after d.
     */
    public boolean isAfter(Date d) {
        return !(this.isBefore(d) == true || (year == d.year && month == d.month && day == d.day));
    }

    /** Returns the number of this Date in the year.
     *  @return a number n in the range 1...366, inclusive, such that this Date
     *  is the nth day of its year.  (366 is only used for December 31 in a leap
     *  year.)
     */
    public int dayInYear() {
        int x = 0;
        if(this.month == 1)
            return this.day;
        if(this.month == 2)
            return 31 + this.day;
        switch (this.month){
            case 3:
                x = 31 + 28 + this.day;
                break;
            case 4:
                x = 31 + 28 + 31 + this.day;
                break;
            case 5:
                x = 31 + 28 + 31 + 30 + this.day;
                break;
            case 6:
                x = 31 + 28 + 31 + 30 + 31 + this.day;
                break;
            case 7:
                x = 31 + 28 + 31 + 30 + 31 + 30 + this.day;
                break;
            case 8:
                x = 31 + 28 + 31 + 30 + 31 + 30 + 31 + this.day;
                break;
            case 9:
                x = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + this.day;
                break;
            case 10:
                x = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + this.day;
                break;
            case 11:
                x = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + this.day;
                break;
            case 12:
                x = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + this.day;
                break;
        }
        if(isLeapYear(this.year))
            return x + 1;
        return x;

    }

    /** Determines the difference in days between d and this Date.  For example,
     *  if this Date is 12/15/1997 and d is 12/14/1997, the difference is 1.
     *  If this Date occurs before d, the result is negative.
     *  @return the difference in days between d and this date.
     */
    public int difference(Date d) {
        int x = 0;
        int i = Math.min(this.year, d.year);
        while (Math.min(this.year, d.year) <= i && i < Math.max(this.year, d.year)){
            if(isLeapYear(i)){
                x += 366;
            }else x += 365;
            i ++;
        }
        if(this.isBefore(d) == true){
            x = -(x - this.dayInYear() + d.dayInYear());
        }else{
            x = x - d.dayInYear() + this.dayInYear();
        }
        return x;
    }

    public static void main(String[] args) {
        System.out.println("\nTesting constructors.");
        Date d1 = new Date(1, 1, 1);
        System.out.println("Date should be 1/1/1: " + d1);
        d1 = new Date("2/4/2");
        System.out.println("Date should be 2/4/2: " + d1);
        d1 = new Date("2/29/2000");
        System.out.println("Date should be 2/29/2000: " + d1);
        d1 = new Date("2/29/1904");
        System.out.println("Date should be 2/29/1904: " + d1);

        d1 = new Date(12, 31, 1975);
        System.out.println("Date should be 12/31/1975: " + d1);
        Date d2 = new Date("1/1/1976");
        System.out.println("Date should be 1/1/1976: " + d2);
        Date d3 = new Date("1/2/1976");
        System.out.println("Date should be 1/2/1976: " + d3);

        Date d4 = new Date("2/27/1977");
        Date d5 = new Date("8/31/2110");

        /* I recommend you write code to test the isLeapYear function! */

        System.out.println("\nTesting before and after.");
        System.out.println(d2 + " after " + d1 + " should be true: " +
                d2.isAfter(d1));
        System.out.println(d3 + " after " + d2 + " should be true: " +
                d3.isAfter(d2));
        System.out.println(d1 + " after " + d1 + " should be false: " +
                d1.isAfter(d1));
        System.out.println(d1 + " after " + d2 + " should be false: " +
                d1.isAfter(d2));
        System.out.println(d2 + " after " + d3 + " should be false: " +
                d2.isAfter(d3));

        System.out.println(d1 + " before " + d2 + " should be true: " +
                d1.isBefore(d2));
        System.out.println(d2 + " before " + d3 + " should be true: " +
                d2.isBefore(d3));
        System.out.println(d1 + " before " + d1 + " should be false: " +
                d1.isBefore(d1));
        System.out.println(d2 + " before " + d1 + " should be false: " +
                d2.isBefore(d1));
        System.out.println(d3 + " before " + d2 + " should be false: " +
                d3.isBefore(d2));

        System.out.println("\nTesting difference.");
        System.out.println(d1 + " - " + d1  + " should be 0: " +
                d1.difference(d1));
        System.out.println(d2 + " - " + d1  + " should be 1: " +
                d2.difference(d1));
        System.out.println(d3 + " - " + d1  + " should be 2: " +
                d3.difference(d1));
        System.out.println(d3 + " - " + d4  + " should be -422: " +
                d3.difference(d4));
        System.out.println(d5 + " - " + d4  + " should be 48762: " +
                d5.difference(d4));
        
    }
}