Date2.java

Below is the syntax highlighted version of Date2.java from §3.3 Designing Data Types.

/******************************************************************************
 *  Compilation:  javac Date.java
 *  Execution:    java Date
 *
 *  ADT for dates (doesn't deal with leap years).
 *
 ******************************************************************************/

public class Date2 {
    private int[] daysInMonth = {
        0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
    };

    private int days;   // days since January 1, 1970

    private Date2(int d) {
        this.days = d;
    }

    public Date2(int month, int day, int year) {
        if (month < 1    || month > 12) throw new RuntimeException("Invalid month");
        if (day   < 1    || day   > 31) throw new RuntimeException("Invalid day");
        if (year  < 1970)               throw new RuntimeException("Invalid year");
        days = (year - 1970) * 365 + (day - 1);
        for (int i = 1; i <= month - 1; i++)
            days += daysInMonth[i];
    }

    // return the next Date
    public Date2 next() { return new Date2(days + 1); }

    // is this Date a after b?
    public boolean isAfter(Date2 b) { return this.days > b.days; }

    public String toString() {
        int year  = 1970 + (days / 365);
        int month, total = 0;
        for (month = 1; month <= 12; month++) {
            total = total + daysInMonth[month];
            if (total > (days % 365)) break;
        }
        int day  = 1 + (days % 365) - total + daysInMonth[month];
        return month + "/" + day + "/" + year;
    }



    // sample client for testing
    public static void main(String[] args) {
        Date2 today = new Date2(12, 25, 2004);
        StdOut.println(today);
        for (int i = 0; i < 1000; i++) {
            today = today.next();
            StdOut.println(today);
        }

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

}