java - 日期的 boolean 编码

Question

class Date {

    private int day;
    private int month;
    private int year;

    public Date() {
    }

    public Date(int day, int month, int year) {
        this.day = day;
        this.month = month;
        this.year = year;
    }

    public int getDay() {
        return this.day;
    }

    public int getMonth() {
        return this.month;
    }

    public int getYear() {
        return this.year;
    }

    public void setDay(int day) {
        day = enteredDay;
    }

    public void setMonth(int month) {
        month = enteredMonth;
    }

    public void setYear(int year) {
        year = enteredYear;
    }

    public String toString() {
        return getDay() + "/" + getMonth() + "/" + getYear();
    }

    public boolean isEarlier(Date) {
        if (enteredDay.getDay() < day) {
            return true;
        } else {
            return false;
        }
    }
}

我无法让最后一种方法发挥作用。它必须是 boolean 值，如果日期早于它，则返回 true。我的问题(至少据我所知)是弄清楚在“<”运算符的两侧写什么。任何有关代码其余部分的反馈将不胜感激。

Answer 1

我会遍历年、月、日，依次进行比较，直到找到严格早或晚的一对。

使用比较器，尤其是在 Java 8 简洁的语法中，可以为您节省大量样板代码:

public boolean isEarlier(Date other) {
    return Comparator.comparingInt(Date::getYear)
                     .thenComparingInt(Date::getMoth)
                     .thenComparingInt(Date::getDay)
                     .compare(this, other) < 0;
}

编辑:
要回答评论中的问题，您当然可以手动比较每个字段:

public boolean isEarlier(Date other) {
    if (getYear() < other.getYear()) {
        return true;
    } else if (getYear() > other.getYear()) {
        return false;
    }

    // If we reached here, both dates' years are equal

    if (getMonth() < other.getMonth()) {
        return true;
    } else if (getMonth() > other.getMonth()) {
        return false;
    }

    // If we reached here, both dates' years and months are equal

    return getDay() < other.getDay();
}

这当然可以压缩为单个 boolean 语句，尽管它是否更优雅或不太优雅在某种程度上取决于情人的眼睛(括号不是严格需要的，但恕我直言，它们使代码更清晰):

public boolean isEarlier(Date other) {
    return (getYear() < other.getYear()) ||
           (getYear() == other.getYear() && 
            getMonth() < other.getMonth()) ||
           (getYear() == other.getYear() && 
            getMonth() == other.getMonth() && 
            getDay() < other.getDay());
}