content: /*************************************************************************
   *  Compilation:  javac Date.java
   *  Execution:    java Date
   *
   *  An immutable data type for dates.
   *
   *************************************************************************/
  
  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
  
      // do bounds-checking to ensure object represents a valid date
      public Date(int month, int day, int year) {
          if (!isValid(month, day, year)) throw new RuntimeException("Invalid date");
          this.month = month;
          this.day   = day;
          this.year  = year;
      }
  
      // create new data by parsing from string of the form mm/dd/yy
      public Date(String date) {
          String[] fields = date.split("/");
          if (fields.length != 3) {
              throw new RuntimeException("Date parse error");
          }
          month = Integer.parseInt(fields[0]);
          day   = Integer.parseInt(fields[1]);
          year  = Integer.parseInt(fields[2]);
          if (!isValid(month, day, year)) throw new RuntimeException("Invalid date");
      }
  
      public int month() { return month; }
      public int day()   { return day;   }
      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;
      }
  
      // return the next Date
      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);
      }
  
  
      // is this Date after b?
      public boolean isAfter(Date b) {
          return compareTo(b) > 0;
      }
  
      // is this Date a before b?
      public boolean isBefore(Date b) {
          return compareTo(b) < 0;
      }
  
      // compare this Date to that one
      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;
      }
  
      // return a string representation of this date
      public String toString() {
          return month + "/" + day + "/" + year;
      }
  
      // is this Date equal to x?
      public boolean equals(Object x) {
          if (x == this) return true;
          if (x == null) return false;
          if (x.getClass() != this.getClass()) return false;
          Date that = (Date) x;
          return (this.month == that.month) && (this.day == that.day) && (this.year == that.year);
      }
  
      public int hashCode() {
          int hash = 17;
          hash = 31*hash + month;
          hash = 31*hash + day;
          hash = 31*hash + year;
          return hash;
      }
  
  
      // sample client for testing
      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);
          }
      }
  
  }
  