java - 调用其他方法和不可变实例

Question

这是考试过去试卷中的一道题。我已经完成了问题并且它有效。但是，我觉得我的实现可能很薄弱，例如我在整个公历类(class)中都使用静态。

我得到了三种方法，可以用我认为合适的任何方式(在公历类(class)中)为每种方法给出一个场景。我对 Gregorian 类中的三个方法使用 static 是否正确。

此外，日、月和年字段应该是不可变的，将它们设置为私有(private)就足够了吗？ (一旦创建，字段值就不能更改)

public class Date {

private int day;// needs to be immutable?
private String month;// needs to be immutable?
private int year;// needs to be immutable?

public Date(int theDay, String theMonth, int theYear) {
    this.day = theDay;
    this.month = theMonth;
    this.year = theYear;
}

public int getDay() {
    return day;
}

public String getMonth() {
    return month;
}

public int getYear() {
    return year;
}

}

公共(public)类公历{

public static Date d;

public static boolean leapYear(){

    if(d.getYear() %400==0 || (d.getYear()%4==0 && d.getYear()%100!=0)){
        return true;
    }else{
        return false;
    }
}

public static int getGregorianDateNumber(){
    int a = (d.getYear()*384)*(32+d.getDay());
    return a;
}

public static int getISO8601Date(){
    int b = (d.getYear()*367)+d.getDay();
    return b;
}

public static void main (String[] args){
    d = new Date(9, "June", 8);
    System.out.println(getGregorianDateNumber());
    System.out.println(getISO8601Date());
    System.out.println(leapYear());
}

}

Answer 1

而不是静态方法和静态字段 d 使它们都是非静态的。

public class Gregorian {
    private final Date d;

    public Gregorian(Date d_) {
        this.d = d_;
    }

    public boolean isLeapyear() {
        ... // implemented as above
    }

    ... // Other methods as above, but all non-static.
}

主要如下:

public static void main (String[] args){
    Date d = new Date(9, "June", 8);
    Gregorian g = new Gregorian(d);
    System.out.println(g.getGregorianDateNumber());
    System.out.println(g.getISO8601Date());
    System.out.println(g.leapYear());
}