算法Sedgewick第四版-第1章基础-003一封装日期

1.

 package ADT;

 import algorithms.util.StdOut;

 /******************************************************************************
  *  Compilation:  javac Date.java
  *  Execution:    java Date
  *  Dependencies: StdOut.java
  *
  *  An immutable data type for dates.
  *
  ******************************************************************************/

 /**
  *  The <tt>Date</tt> class is an immutable data type to encapsulate a
  *  date (day, month, and year).
  *  <p>
  *  For additional documentation,
  *  see <a href="http://algs4.cs.princeton.edu/12oop">Section 1.2</a> of
  *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
  *
  *  @author Robert Sedgewick
  *  @author Kevin Wayne
  */
 public class Date implements Comparable<Date> {
     private static final int[] DAYS = { 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

     private final int month;   // month (between 1 and 12)
     private final int day;     // day   (between 1 and DAYS[month]
     private final int year;    // year

    /**
      * Initializes a new date from the month, day, and year.
      * @param month the month (between 1 and 12)
      * @param day the day (between 1 and 28-31, depending on the month)
      * @param year the year
      * @throws IllegalArgumentException if this date is invalid
      */
     public Date(int month, int day, int year) {
         if (!isValid(month, day, year)) throw new IllegalArgumentException("Invalid date");
         this.month = month;
         this.day   = day;
         this.year  = year;
     }

     /**
      * Initializes new date specified as a string in form MM/DD/YYYY.
      * @param date the string representation of this date
      * @throws IllegalArgumentException if this date is invalid
      */
     public Date(String date) {
         String[] fields = date.split("/");
         if (fields.length != 3) {
             throw new IllegalArgumentException("Invalid date");
         }
         month = Integer.parseInt(fields[0]);
         day   = Integer.parseInt(fields[1]);
         year  = Integer.parseInt(fields[2]);
         if (!isValid(month, day, year)) throw new IllegalArgumentException("Invalid date");
     }

     /**
      * Return the month.
      * @return the month (an integer between 1 and 12)
      */
     public int month() {
         return month;
     }

     /**
      * Returns the day.
      * @return the day (an integer between 1 and 31)
      */
     public int day() {
         return day;
     }

     /**
      * Returns the year.
      * @return the year
      */
     public int year() {
         return year;
     }

     // is the given date valid?
     private static boolean isValid(int m, int d, int y) {
         if (m < 1 || m > 12)      return false;
         if (d < 1 || d > DAYS[m]) return false;
         if (m == 2 && d == 29 && !isLeapYear(y)) return false;
         return true;
     }

     // is y a leap year?
     private static boolean isLeapYear(int y) {
         if (y % 400 == 0) return true;
         if (y % 100 == 0) return false;
         return y % 4 == 0;
     }

     /**
      * Returns the next date in the calendar.
      *
      * @return a date that represents the next day after this day
      */
     public Date next() {
         if (isValid(month, day + 1, year))    return new Date(month, day + 1, year);
         else if (isValid(month + 1, 1, year)) return new Date(month + 1, 1, year);
         else                                  return new Date(1, 1, year + 1);
     }

     /**
      * Compares two dates chronologically.
      *
      * @param  that the other date
      * @return <tt>true</tt> if this date is after that date; <tt>false</tt> otherwise
      */
     public boolean isAfter(Date that) {
         return compareTo(that) > 0;
     }

     /**
      * Compares two dates chronologically.
      *
      * @param  that the other date
      * @return <tt>true</tt> if this date is before that date; <tt>false</tt> otherwise
      */
     public boolean isBefore(Date that) {
         return compareTo(that) < 0;
     }

     /**
      * Compares two dates chronologically.
      *
      * @return the value <tt>0</tt> if the argument date is equal to this date;
      *         a negative integer if this date is chronologically less than
      *         the argument date; and a positive ineger if this date is chronologically
      *         after the argument date
      */
     @Override
     public int compareTo(Date that) {
         if (this.year  < that.year)  return -1;
         if (this.year  > that.year)  return +1;
         if (this.month < that.month) return -1;
         if (this.month > that.month) return +1;
         if (this.day   < that.day)   return -1;
         if (this.day   > that.day)   return +1;
         return 0;
     }

     /**
      * Returns a string representation of this date.
      *
      * @return the string representation in the format MM/DD/YYYY
      */
     @Override
     public String toString() {
         return month + "/" + day + "/" + year;
     }

     /**
      * Compares this date to the specified date.
      *
      * @param  other the other date
      * @return <tt>true</tt> if this date equals <tt>other</tt>; <tt>false</tt> otherwise
      */
     @Override
     public boolean equals(Object other) {
         if (other == this) return true;
         if (other == null) return false;
         if (other.getClass() != this.getClass()) return false;
         Date that = (Date) other;
         return (this.month == that.month) && (this.day == that.day) && (this.year == that.year);
     }

     /**
      * Returns an integer hash code for this date.
      *
      * @return a hash code for this date
      */
     @Override
     public int hashCode() {
         int hash = 17;
         hash = 31*hash + month;
         hash = 31*hash + day;
         hash = 31*hash + year;
         return hash;
     }

     /**
      * Unit tests the <tt>Date</tt> data type.
      */
     public static void main(String[] args) {
         Date today = new Date(2, 25, 2004);
         StdOut.println(today);
         for (int i = 0; i < 10; i++) {
             today = today.next();
             StdOut.println(today);
         }

         StdOut.println(today.isAfter(today.next()));
         StdOut.println(today.isAfter(today));
         StdOut.println(today.next().isAfter(today));

         Date birthday = new Date(10, 16, 1971);
         StdOut.println(birthday);
         for (int i = 0; i < 10; i++) {
             birthday = birthday.next();
             StdOut.println(birthday);
         }
     }

 }