学习体会：简单的代码也要写得美

今天做了到简单的泛型练习题，自己先敲完实现了，再去看老师的答案，简直羡慕死我，老师的代码看着 “ 太美了 ” 。题目如下：

这是道很简单的练习题，涉及前面所学的ArrayList中sort方法的定制排序，即重写传入的接口的compare方法。下面是我的实现方法：

日期类MyDate：

class MyDate {
    private int year;
    private int month;
    private int day;

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

    public static int compareDate(MyDate date1, MyDate date2) {
        if (date1.getYear() == date2.getYear()) {
            if (date1.getMonth() == date2.getMonth()) {
                if (date1.getDay() > date2.getDay()) {
                    return 1;
                } else {
                    return -1;
                }
            } else if (date1.getMonth() > date2.getMonth()) {
                return 1;
            } else {
                return -1;
            }
        } else if (date1.getYear() > date2.getYear()) {
            return 1;
        } else {
            return -1;
        }
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getMonth() {
        return month;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        this.day = day;
    }
}

员工类Employee：

class Employee {
    private String name;
    private double sal;
    private MyDate birthday;

    @SuppressWarnings({"all"})
    public Employee(String name, double sal, MyDate birthday) {
        this.name = name;
        this.sal = sal;
        this.birthday = birthday;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getSal() {
        return sal;
    }

    public void setSal(double sal) {
        this.sal = sal;
    }

    public MyDate getBirthday() {
        return birthday;
    }

    public void setBirthday(MyDate birthday) {
        this.birthday = birthday;
    }

    @Override
    public String toString() {
        return name + " " + sal + " " + birthday.getYear() + "-"
                + birthday.getMonth() + "-" + birthday.getDay();
    }
}

测试类Demo：

public class Demo {
    @SuppressWarnings({"all"})
    public static void main(String[] args) {
        ArrayList emlist = new ArrayList<>();
        Employee em1 = new Employee("JJLin", 34000, new MyDate(1989, 3, 23));
        Employee em2 = new Employee("GEA", 24005, new MyDate(1995, 4, 12));
        Employee em3 = new Employee("Jack", 45098, new MyDate(1994, 12, 10));

        emlist.add(em1);
        emlist.add(em2);
        emlist.add(em3);
        System.out.println(emlist);

        emlist.sort(new Comparator() {
            @Override
            public int compare(Employee o1, Employee o2) {
                
                if (o1.getName().compareTo(o2.getName()) > 0) {
                    return 1;
                } else if (o1.getName().compareTo(o2.getName()) < 0) {
                    return -1;
                } else {
                    return MyDate.compareDate(o1.getBirthday(), o2.getBirthday());
                }
            }
        });

        System.out.println(emlist);
    }
}

我将日期的比较封装成一个MyDate类中的方法，这样看也没错，功能也确实能实现，但缺点很明显：代码冗余度较高、可读性不够。下面是老师对于日期比较的代码：

class MyDate implements Comparable{//老师实现了Comparable接口
    private int year;
    private int month;
    private int day;

//该类除MyDate实现了Comparable接口、原先的
//compareDate方法替换成compareTo, 其余代码不变

    @Override
    public int compareTo(MyDate date) {
        int yearMinus = this.year - date.year;
        if (yearMinus != 0){
            return yearMinus;
        }

        int monthMinus = this.year - date.year;
        if (monthMinus != 0) {
            return monthMinus;
        }

        int dayMinus = this.day - date.day;
        if (dayMinus != 0) {
            return dayMinus;
        }

        return 0;
    }
}

main方法中，只看定制排序部分，其余不变：

emlist.sort(new Comparator() {
            @Override
            public int compare(Employee o1, Employee o2) {
                
                int nameres = o1.getName().compareTo(o2.getName());
                if (nameres != 0){
                    return nameres;
                }
                return o1.getBirthday().compareTo(o2.getBirthday());
            }
        });

自己对日期判断用了 if - else 分支结构，但没用好，反而让代码量增加，阅读体验感不佳。老师的代码值得学习的地方：

1. 利用好比较值的差值，作返回值，减少代码量，逻辑更清晰；

2. 让日期类实现Comparable接口，使后续有日期比较，都可用重写的该方法；

在这记录下，方便日后复习