IDI Software Component Library
© 1999 Information Disciplines, Inc., Chicago

Date and Calendar package (Java Class Definitions)

Most business applications and many scientific applications need to manipulate dates. Unfortunately, Java's amateurish "standard" library classes are unsuited to serious application programming, because:

• they don't support essential functionality for most users,
• their unnatural public interface is clumsy and error-prone, and
• they violate fundamental object-oriented principles.

On the other hand this easy-to-use package provides in a natural way the date functionality that typical business and scientific applications need. It allows applications to avoid the ugly Java classes.

Usage

Three classes

The package consists of three classes.

   Date(int yyyy, int mm, int dd) // Year, month, day
   Date(int yyyy, int ddd)        // Year and day number
   Date(final Date x)             // Copy constructor
   Date()                         // (undefined default value)
   Date(final String yymmdd)      // See note #1

Note 1: The fifth constructor, using the one-time ANSI "standard" 6-character representation, uses the windowing parameter in the CalendarInfo class to determine the century.

Accessor functions

   short d.weekday()      //  Day of week (0=Sunday, 6=Saturday)

For efficiency, the following four functions decompose a date into its Gregorian components and cache those components for later retrieval by the other functions. (Warning: This caching logic has not been exhaustively validated for multithreaded invocation.)

    int   d.year()
    int   d.month()       //  1=January, 12=December
    int   d.day()         //  Day of the month
    int   d.dayno()       //  Day number within year

Arithmetic and relational operator functions

Days class

This class complements the Date class as the corresponding extent in time or relative date. It arises naturally and inevitably from the subtraction of one date from another. Programmers who need a finer-grained duration class are invited to call us at 1-773 736-9661.

Constructors

    Days(int n)
    Days()                     //  Default value = 0
    Days(final Days x)         //  Copy constructor

Arithmetic and relational operator functions

CalendarInfo class

The static data and functions in this class are used by various methods in the Date class and by some client programs. This class has no knowledge of the Date class or of the internal representation of Date objects.

Constants and tables

Integer constants for calendar computations

      DAYS_PER_YEAR
      DAYS_PER_4_YEARS
      DAYS_PER_100_YEARS
      DAYS_PER_400_YEARS

Integer tables (for non leap years)

     DAYS_IN_MONTH[]      // See note #2
     DAYS_BEFORE_MONTH[]  //  See note #2 

String-valued language-specific (English) name tables

     MONTH_NAME[]  // See note #2
     DAY_NAME      // 0=Sunday, 6=Saturday

Note 2: Month tables are subscripted by the number of the month, 1-12. (The 0-elements are unused.) Thus DAYS_BEFORE_MONTH[9] is 243 and MONTH_NAME[9] is "September".

User-overridable "windowing" parameter

This parameter defines the interpretation of two-digit (modulo 100) years. It is used by one of the Date class constructors and by some client programs.

  short centuryBreak // default=20

Static functions

These functions provide Gregorian calendar logic:

   boolean  isLeapYear(int yyyy)
   boolean  isLegalYMD(int yyyy, int mm, int dd)
   short    dayNumber (int yyyy, int mm, int dd)    //  Day number within the year