date.java

public class Date_My {
    private final int value;
    public Date_My(int year, int month, int day){
        value = year*512 + month*32 + day;
        // value = y * 2^9 + m * 2^5+ d;
    }
    public int month(){
        return (value / 32) % 16;
        // 除以32后，剩下 y*2^4 + m（d消掉了，2^4 = 2^9 / 2^5），接着再用16(即2^4)取余,得month
    }
    public int day(){
        return value % 32;
        // 用32取余自然得到余数day
    }
    public int year(){
        return value / 512;
        // 用512取余自然得到余数year
    }
    public String toString(){
        return month() + "/" + day() + "/" +year();
    }

    public static void main(String args[]){
        Date_My date = new Date_My(2015, 10, 15);
        StdOut.println(date.year());
        StdOut.println(date.month());
        StdOut.println(date.day());
    }
}