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Add code of "DateUtil" task
Add code of "DateUtil" task
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‎difficult/DateUtil.java

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/**
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* Complete the following methods in a class called DateUtil:
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*
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* - boolean isLeapYear(int year): returns true if the given year is a leap year.
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* A year is a leap year if it is divisible by 4 but not by 100, or it is divisible by 400.
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*
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* - boolean isValidDate(int year, int month, int day): returns true if the given year,
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* month and day constitute a given date. Assume that year is between 1 and 9999,
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* month is between 1 (Jan) to 12 (Dec) and day shall be between 1 and 28|29|30|31
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* depending on the month and whether it is a leap year.
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*
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* - int getDayOfWeek(int year, int month, int day): returns the day of the week,
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* where 0 for SUN, 1 for MON, ..., 6 for SAT, for the given date. Assume that the date is valid.
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*
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* - String toString(int year, int month, int day): prints the given date
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* in the format "xxxday d mmm yyyy", e.g., "Tuesday 14 Feb 2012". Assume that the given date is valid.
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*
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* To find the day of the week (Reference: Wiki "Determination of the day of the week"):
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* 1. Based on the first two digit of the year, get the number from the following "century" table.
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* -------+---------+--------+--------+--------+--------+--------+--------+
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* 1700- | 1800- | 1900- | 2000- | 2100- | 2200- | 2300- | 2400- |
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* 4 | 2 | 0 | 6 | 4 | 2 | 0 | 6 |
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* -------+---------+--------+--------+--------+--------+--------+--------+
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* Take note that the entries 4, 2, 0, 6 repeat.
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*
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* 2. Add to the last two digit of the year.
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*
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* 3. Add to "the last two digit of the year divide by 4, truncate the fractional part".
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*
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* 4. Add to the number obtained from the following month table:
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* -------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
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* Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
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* -------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
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* Non-Leap Year 0 | 3 | 3 | 6 | 1 | 4 | 6 | 2 | 5 | 0 | 3 | 5 |
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* -------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
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* Leap Year 6 | 2 | same as above |
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* -------------------+-----+-----------------------------------------------------------+
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*
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* 5. Add to the day.
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*
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* 6. The sum modulus 7 gives the day of the week, where 0 for SUN, 1 for MON, ..., 6 for SAT.
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*
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* For example: 2012, Feb, 17
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* (6 + 12 + 12/4 + 2 + 17) % 7 = 5 (Fri)
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*/
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package javaexercises.difficult;
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public class DateUtil {
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private final int MIN_YEAR = 1;
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private final int MAX_YEAR = 9999;
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// Month's name – for printing
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private final String[] strMonths = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
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"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
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// Day's name - for printing
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private final String[] strDays = {"Sunday", "Monday", "Tuesday", "Wednesday",
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"Thursday", "Friday", "Saturday"};
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// Number of days in each month (for non-leap years)
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private final int[] daysInMonths = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
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private final int[] nonLeapYearMonthNumbers = {0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5};
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private final int[] leapYearMonthNumbers = {6, 2, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5};
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public static void main(String[] args) {
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DateUtil aDateUtil = new DateUtil();
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System.out.println(aDateUtil.isLeapYear(1900)); // false
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System.out.println(aDateUtil.isLeapYear(2000)); // true
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System.out.println(aDateUtil.isLeapYear(2011)); // false
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System.out.println(aDateUtil.isLeapYear(2012)); // true
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System.out.println(aDateUtil.isValidDate(2012, 2, 29)); // true
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System.out.println(aDateUtil.isValidDate(2011, 2, 29)); // false
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System.out.println(aDateUtil.isValidDate(2099, 12, 31)); // true
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System.out.println(aDateUtil.isValidDate(2099, 12, 32)); // false
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System.out.println(aDateUtil.getDayOfWeek(1982, 4, 24)); // 6:Sat
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System.out.println(aDateUtil.getDayOfWeek(2000, 1, 1)); // 6:Sat
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System.out.println(aDateUtil.getDayOfWeek(2054, 6, 19)); // 5:Fri
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System.out.println(aDateUtil.getDayOfWeek(2012, 2, 17)); // 5:Fri
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System.out.println(aDateUtil.toString(2012, 2, 14)); // Tuesday 14 Feb 2012
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System.out.println(aDateUtil.toString(2014, 2, 26)); // Wednesday 26 Feb 2014
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}
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/**
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* Returns true if the given year is a leap year.
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* A year is a leap year if it is divisible by 4 but not by 100,
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* or it is divisible by 400.
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*
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* @param year
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* @return true if the given year is a leap year.
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*/
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private boolean isLeapYear(int year) {
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return (year%4 == 0 && year%100 != 0) || (year%400 == 0);
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}
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/**
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* Returns true if the given year, month and day constitute a given date.
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* Assume that year is between 1 and 9999, month is between 1 (Jan) to 12 (Dec)
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* and day shall be between 1 and 28|29|30|31 depending on the month
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* and whether it is a leap year.
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*
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* @param year
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* @param month
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* @param day
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* @return true if the given year, month and day constitute a given date.
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*/
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private boolean isValidDate(int year, int month, int day)
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{
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if (year < MIN_YEAR || year > MAX_YEAR) {
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return false;
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}
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if (month < 1 || month > 12) {
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return false;
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}
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int monthDays = daysInMonths[month-1] + (month == 2 && isLeapYear(year) ? 1 : 0);
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return 1 <= day && day <= monthDays;
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}
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// Return the day of the week, 0:Sun, 1:Mon, ..., 6:Sat
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private int getDayOfWeek(int year, int month, int day)
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{
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// 1. Based on the first two digit of the year, get the number from the "century" table.
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int magicCenturyNumber = 6 - 2*((year / 100) % 4);
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// 2. Add to the last two digit of the year.
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int lastTwoDigitsOfYear = year % 100;
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// 3. Add to "the last two digit of the year divide by 4, truncate the fractional part".
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int magicYearNumber = lastTwoDigitsOfYear / 4;
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// 4. Add to the number obtained from the month table.
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int magicMonthNumber = isLeapYear(year) ? leapYearMonthNumbers[month-1] : nonLeapYearMonthNumbers[month-1];
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// 5. Add to the day.
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int magicDayNumber = day;
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// 6. The sum modulus 7 gives the day of the week, where 0 for SUN, 1 for MON, ..., 6 for SAT.
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return ( magicCenturyNumber + lastTwoDigitsOfYear
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+ magicYearNumber + magicMonthNumber + magicDayNumber) % 7;
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}
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// Return String "xxxday d mmm yyyy" (e.g., Wednesday 29 Feb 2012)
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private String toString(int year, int month, int day) {
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if ( ! isValidDate(year, month, day)) {
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return "Not a valid date!";
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}
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int d = getDayOfWeek(year, month, day);
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return strDays[d] + " " + day + " " + strMonths[month-1] + " " + year;
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}
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}

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