子类问题（JAVA）

Question

我有一个类 Appointment 有字段：

• int day
• int month
• int year
• String desc

这会存储约会的描述以及日期。

超级班Appointment：

public class Appointment {
    int dayNum;
    int monthNum;
    int yearNum;
    String desc;

    public Appointment(String des, int day) {
        //Monthly Appointments (Check day)
        desc = des;
        dayNum = day;
    }
    public Appointment(String des, int day, int month){
        //Yearly Appointments (Check day AND month)   
        desc = des;
        dayNum = day;
        monthNum = month;
    }
    public Appointment(String des, int day, int month, int year){
        //One Time (Check All)
        desc = des;
        dayNum = day;
        monthNum = month;
        yearNum = year;
    }     
}

这是我的 3 个子类：

一次性约会：Onetime

public class OneTime extends Appointment{
    public OneTime(String des, int day, int month, int year){
        super(des, day, month, year);
    }
    public String getDesc(){
        return desc;
    }
}

每月一次约会：Monthly

public class Monthly extends Appointment{
    public Monthly(String des, int monum){
        super(des, monum);
    }
    public String getDesc(){
        return desc;
    }
}

每年一次约会 Yearly

public class Yearly extends Appointment{
    public Yearly(String des, int day, int month){
        super(des, day, month);
    }
    public String getDesc(){
        return desc;
    }
}

问题： 我被要求将一些不同的Appointment 对象添加到ArrayList（我知道）。但是，我必须编写一个方法occursOn(int day, int month, int year) 来返回当天的所有约会。我不确定的部分是编写occursOn() 方法。假设我有一个 11/22/2018 的约会，我如何将 Monthly 对象与 day 参数/Yearly 与月和日参数/OneTime 与所有参数进行比较？

教科书问题： " 实现超类 Appointment 和子类 Onetime、Daily 和 Monthly。约会有描述（例如，“看牙医”）和一个日期。写一个方法occursOn(int year, int month, int day)来检查约会是否发生在那个日期。例如，对于每月约会，你必须检查当月的日期是否匹配。然后用一个Appointment对象的数组填充一个约会的混合。让用户输入一个日期并打印出该日期发生的所有约会。"

注意：这不是我的作业。我只是在 2 小时内对此进行了单元测试，然后卡住了。

Answer 1

首先，你可能想声明Appointment abstract，这样子类必须实现一些方法：

 public abstract class Appointment {

        int dayNum;
        int monthNum;
        int yearNum;
        String desc;

        public Appointment(String des, int day){desc = des; dayNum = day;} //Monthly Appointments (Check day)
        public Appointment(String des, int day, int month){desc = des; dayNum = day; monthNum = month;} //Yearly Appointments (Check day AND month)   
        public Appointment(String des, int day, int month, int year){desc = des; dayNum = day; monthNum = month; yearNum = year;} //One Time (Check All)    

        abstract boolean occursOn(int day, int month, int year);

        abstract String getDesc();

        }

那么，occursOn 在你的类中的实现可能是：

每月

    boolean occursOn(int day, int month, int year){

                return (this.day == day);
}

每年

    boolean occursOn(int day, int month, int year){

        return (this.day == day) && (this.month == month);
}

一次性

    boolean occursOn(int day, int month, int year){

                return (this.day == day) && (this.month == month) && (this.year == year);
}

最后，假设appointments 是一个List，你填充了子类的各种实例，有一个通用方法（可能在你的主类中），它将返回所有对应Appointment 对象的列表：

public List<Appointment> occursOn(int year, int month, int day){

List<Appointment> result = new ArrayList<Appointment>();

  for(Appointment appointment : appointments){

    if(appointment.occursOn(year, month, day))
      result.add(appointment);
  }

return result;

}

Answer 2

OccursOn()

应该是超类（Appointment）中的一个抽象方法。 您的每个子类都必须相应地实现它。

一次性 - 检查日、月和年。

每月 - 仅检查日期。

每年 - 检查日期和月份。

Answer 3

一种方法是使用带有可选值的“日期”键的地图，例如像这样：

class DateKey {
  int day; //always needed
  Integer month; //null in case of monthlies
  Integer year; //null in case of monthlies and yearlies

  //override equals() and hashCode()
}

对地图使用日期键：

//handling this would be easier with Google Guava's Multimap, if you may use it
Map<DateKey, List<Appointment>> appointments = ...;

然后您使用 3 步查找：

List<Appointment> onetimes = appointments.get(new DateKey( day, month, year) );
List<Appointment> yearlies= appointments.get(new DateKey( day, month, null) );
List<Appointment> monthlies = appointments.get(new DateKey( day, null, null) );

最后合并 3 个列表。

最后，DateKey 也可以是Appointment 类的一部分，这将使映射更加一致。我可能会使用一个稍微不同的名称（想想一个），因为它不再只是一个地图键。

Answer 4

您可以向您的 Appointment 类添加一个方法，以确定 Appointment 是否在这样的给定日期开启。

public class Appointment {

    int dayNum;
    int monthNum;
    int yearNum;
    String desc;

    public Appointment(String des, int day){desc = des; dayNum = day;} //Monthly Appointments (Check day)
    public Appointment(String des, int day, int month){desc = des; dayNum = day; monthNum = month;} //Yearly Appointments (Check day AND month)
    public Appointment(String des, int day, int month, int year){desc = des; dayNum = day; monthNum = month; yearNum = year;} //One Time (Check All)

    boolean occuresOn(int day, int month, int year){
        if( (this.dayNum == day) && (this.monthNum == month) && (this.yearNum == year))
            return true;

        return false;

    }
}

并在子类中覆盖此功能。

public class Monthly extends Appointment{

    public Monthly(String des, int monum){
        super(des, monum);
    }
    public String getDesc(){
        return desc;
    }

    boolean occuresOn(int day, int month, int year){
        if( (this.dayNum == day) )
            return true;

        return false;

    }
}

public class Yearly extends Appointment{

    public Yearly(String des, int day, int month){
        super(des, day, month);
    }
    public String getDesc(){
        return desc;
    }

    boolean occuresOn(int day, int month, int year){
        if( (this.dayNum == day) && (this.monthNum == month))
            return true;

        return false;

    }
}

现在您可以遍历您的约会并找到约会中的约会：

List<Appointment> aps = new ArrayList<>(); //initialize this
    for (Appointment ap : aps){
        if(ap.occuresOn(2, 3, 2016))
            ....
    }