Clean Code

Appendix B: 
org.jfree.date.SerialDate
63 * 1-Jan-1900 to 31-Dec-9999.
64 *
65 * Be aware that there is a deliberate bug in Excel that recognises the year
66 * 1900 as a leap year when in fact it is not a leap year. You can find more
67 * information on the Microsoft website in article Q181370:
68 *
69 * http://support.microsoft.com/support/kb/articles/Q181/3/70.asp
70 *
71 * Excel uses the convention that 1-Jan-1900 = 1. This class uses the
72 * convention 1-Jan-1900 = 2.
73 * The result is that the day number in this class will be different to the
74 * Excel figure for January and February 1900...but then Excel adds in an extra
75 * day (29-Feb-1900 which does not actually exist!) and from that point forward
76 * the day numbers will match.
77 *
78 * @author David Gilbert
79 */
80 public class SpreadsheetDate extends SerialDate {
81 
82 /** For serialization. */
83 private static final long serialVersionUID = -2039586705374454461L;
84 
85 /**
86 * The day number (1-Jan-1900 = 2, 2-Jan-1900 = 3, ..., 31-Dec-9999 =
87 * 2958465).
88 */
89 private int serial;
90 
91 /** The day of the month (1 to 28, 29, 30 or 31 depending on the month). */
92 private int day;
93 
94 /** The month of the year (1 to 12). */
95 private int month;
96 
97 /** The year (1900 to 9999). */
98 private int year;
99 
100 /** An optional description for the date. */
101 private String description;
102 
103 /**
104 * Creates a new date instance.
105 *
106 * @param day the day (in the range 1 to 28/29/30/31).
107 * @param month the month (in the range 1 to 12).
108 * @param year the year (in the range 1900 to 9999).
109 */
110 public SpreadsheetDate(final int day, final int month, final int year) {
111 
112 if ((year >= 1900) && (year <= 9999)) {
113 this.year = year;
114 }
115 else {
116 throw new IllegalArgumentException(
117 "The 'year' argument must be in range 1900 to 9999."
118 );
119 }
120 
121 if ((month >= MonthConstants.JANUARY)
122 && (month <= MonthConstants.DECEMBER)) {
123 this.month = month;
124 }