java - 一种找出两个日期之间的差异的方法

Question

我的方法有效，因为我只想知道年份的差异，我的问题是我这样做效率很低。我觉得有一种更简单、更美观的方法来编写该方法。

编辑:我必须编写自己的方法。我也不想特意使用高级东西，一些在第一年程序员范围内的东西。

public int differenceInYears(MyDate comparedDate) {
        int difference = 0;
        if (this.year > comparedDate.year) {
            if (this.month > comparedDate.month) {
                difference = this.year - comparedDate.year;
            }
            else if (this.month == comparedDate.month) {
                if (this.day >= comparedDate.day) {
                    difference = this.year - comparedDate.year;
                }
                else {
                    difference = this.year - comparedDate.year - 1;
                }
            }
            else {
                difference = this.year - comparedDate.year - 1;
            }
        }
        if (comparedDate.year > this.year) {
            if (comparedDate.month > this.month) {
                difference = comparedDate.year - this.year;
            }
            else if (comparedDate.month == this.month) {
                if (comparedDate.day >= this.day) {
                    difference = comparedDate.year - this.year;
                }
                else {
                    difference = comparedDate.year - this.year - 1;
                }
            }
            else {
                difference = comparedDate.year - this.year - 1;
            }
        }
        return difference;
    }

我将在下面为上下文添加 MyDate 类:

public class MyDate {

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

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

    public String toString() {
        return this.day + "." + this.month + "." + this.year;
    }

    public boolean earlier(MyDate compared) {
        if (this.year < compared.year) {
            return true;
        }

        if (this.year == compared.year && this.month < compared.month) {
            return true;
        }

        if (this.year == compared.year && this.month == compared.month
                && this.day < compared.day) {
            return true;
        }

        return false;
    }

Answer 1

我会假定您的方法工作正常。如何改进？您可以做的第一件事是消除所有重复的 this.year - comparedDate.year 和 comparedDate.year - this.year 计算。无论如何你都要做它们，所以让我们把它们放在各自的 if block 的顶部。

public int differenceInYears(MyDate comparedDate) {
    int difference;

    if (this.year > comparedDate.year) {
        difference = this.year - comparedDate.year;

        if (this.month > comparedDate.month) {
        }
        else if (this.month == comparedDate.month) {
            if (this.day >= comparedDate.day) {
            }
            else {
                difference -= 1;
            }
        }
        else {
            difference -= 1;
        }
    }
    if (comparedDate.year > this.year) {
        difference = comparedDate.year - this.year;

        if (comparedDate.month > this.month) {
        }
        else if (comparedDate.month == this.month) {
            if (comparedDate.day >= this.day) {
            }
            else {
                difference -= 1;
            }
        }
        else {
            difference -= 1;
        }
    }

    return difference;
}

接下来，让我们去掉那些空的分支。

public int differenceInYears(MyDate comparedDate) {
    int difference;

    if (this.year > comparedDate.year) {
        difference = this.year - comparedDate.year;

        if (this.month == comparedDate.month) {
            if (this.day < comparedDate.day) {
                difference -= 1;
            }
        }
        else if (this.month < comparedDate.month) {
            difference -= 1;
        }
    }
    if (comparedDate.year > this.year) {
        difference = comparedDate.year - this.year;

        if (comparedDate.month == this.month) {
            if (comparedDate.day < this.day) {
                difference -= 1;
            }
        }
        else if (comparedDate.month < this.month) {
            difference -= 1;
        }
    }

    return difference;
}

现在让我们看看我们是否不能用 && 和 || 将一些条件压缩在一起。

public int differenceInYears(MyDate comparedDate) {
    int difference;

    if (this.year > comparedDate.year) {
        difference = this.year - comparedDate.year;

        if (this.month == comparedDate.month && this.day < comparedDate.day ||
            this.month < comparedDate.month)
        {
            difference -= 1;
        }
    }
    if (comparedDate.year > this.year) {
        difference = comparedDate.year - this.year;

        if (comparedDate.month == this.month && comparedDate.day < this.day ||
            comparedDate.month < this.month)
        {
            difference -= 1;
        }
    }

    return difference;
}

这两个街区看起来非常相似，不是吗？我们可以通过有条件地交换 this 和 comparedDate 来组合它们。设 a 和 b 分别是较早和较晚的日期。

public int differenceInYears(MyDate comparedDate) {
    MyDate a = (this.year < comparedDate.year) ? this : comparedDate;
    MyDate b = (this.year < comparedDate.year) ? comparedDate : this;

    int difference = b.year - a.year;

    if (a.year < b.year) {
        if (a.month == b.month && a.day < b.day ||
            a.month < b.month)
        {
            difference -= 1;
        }
    }

    return difference;
}

还有最后的挤压。

public int differenceInYears(MyDate comparedDate) {
    MyDate a = (this.year < comparedDate.year) ? this : comparedDate;
    MyDate b = (this.year < comparedDate.year) ? comparedDate : this;

    int difference = b.year - a.year;

    if (a.year < b.year &&
       (a.month == b.month && a.day < b.day ||
        a.month < b.month))
    {
        difference -= 1;
    }

    return difference;
}