import java.util.TimeZone; /** Objects of the Date class represent calendar dates such as March 14, 1997. @author Marty Stepp @version 1.0 */ public class Date { // constants private static final int JANUARY = 1; private static final int FEBRUARY = 2; private static final int DECEMBER = 12; private static final int DAYS_PER_WEEK = 7; private static final int DAYS_PER_YEAR = 365; private static final int DAYS_PER_LEAP_YEAR = 366; private static final String[] DAY_NAMES = {"SUNDAY", "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY", "SATURDAY"}; private static final int[] DAYS_PER_MONTH = { -1, // 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, }; // fields private int year; private int month; private int day; /** Constructs a new object representing the given year, month, and day. @throws IllegalArgumentException if month is not between 1 and 12, or if day is not between 1 and the number of days in that month. */ public Date(int year, int month, int day) { this.year = year; this.month = month; this.day = day; if (month < 1 || month > 12 || day < 1 || day > getDaysInMonth()) { throw new IllegalArgumentException("Invalid day or month: " + toString()); } } /** Constructs a new object representing today's date. */ public Date() { this(1970, JANUARY, 1); int daysSinceEpoch = (int) ((System.currentTimeMillis() + TimeZone.getDefault().getRawOffset()) / 1000 / 60 / 60 / 24); for (int i = 0; i < daysSinceEpoch; i++) { nextDay(); } } /** Adds the given number of days to this Date. @throws IllegalArgumentException if days < 0. */ public void addDays(int days) { while (days > getDaysInYear()) { days -= getDaysInYear(); year++; } for (int i = 1; i <= days; i++) { nextDay(); } } /** Returns whether o refers to a Date object representing the same year, month, and day as this one. */ public boolean equals(Object o) { Date other = (Date) o; return day == other.day && month == other.month && year == other.year; } /** Returns the day represented by this Date object. @return the day, between 1 and the number of days in this Date's month (which varies from 28 to 31) */ public int getDay() { return day; } /** Returns the number of days in the month represented by the current Date. */ public int getDaysInMonth() { int result = DAYS_PER_MONTH[month]; if (month == FEBRUARY && isLeapYear()) { result++; } return result; } public int getDaysInYear() { if (isLeapYear()) { return 366; } else { return 365; } } /** Returns a string such as "Monday" representing what day of the week this Date fell on. @return the day as either "Sunday", "Monday", "Tuesday, "Wednesday", "Thursday", "Friday", or "Saturday" */ public String getDayOfWeek() { int index = 1; Date temp = new Date(1753, JANUARY, 1); while (temp != this) { temp.nextDay(); index = (index + 1) % DAYS_PER_WEEK; } return DAY_NAMES[index]; } /** Returns the month represented by this Date object. @return the month, between 1 and 12 */ public int getMonth() { return month; } /** Returns the year represented by this Date object. @return the year */ public int getYear() { return year; } /** Returns whether this Date falls on a leap year. @return true if in a year divisible by 4 but not by 100 unless by 400 */ public boolean isLeapYear() { return (year % 400 == 0) || (year % 4 == 0 && year % 100 != 0); } /** Advances this Date to the next day. If necessary, wraps to the next month and/or year. */ public void nextDay() { day++; if (day > getDaysInMonth()) { // wrap to next month month++; day = 1; if (month > DECEMBER) { // wrap to next year year++; month = JANUARY; } } } /** Returns a String representation of this Date. @return a String such as "2007/07/26" for July 26, 2007 */ public String toString() { return year + "/" + pad(month) + "/" + pad(day); } private String pad(int n) { if (n < 10) { return "0" + n; } else { return "" + n; } } }