使用Comparator命令ArrayList Java

Question

我必须按日期和时间订购约会.我有一个约会的ArrayList,并试图创建一个比较器来比较他们的日期和时间.我正在尝试使用Collections.sort方法,将其传递给Appointments的ArrayList和我创建的AppointmentComparator.在编译时,我得到了"没有合适的排序方法".以下是编译器生成的完整错误消息的链接:http://prntscr.com/7y4qb

比较:

public class AppointmentComparator implements Comparator<Appointment>
{
public int compare(Appointment a, Appointment b)
{
    if (a.getDay() < b.getDay())
        return -1;

    if (a.getDay() == b.getDay())
    {
        if (a.getStart() < b.getStart())
            return -1;
        if (a.getStart() > b.getStart())
            return 1;
        return 0;
    }

    return 1;
}

带语法错误的行:

Collections.sort(book, new AppointmentComparator());

变量book是约会的ArrayList. ArrayList<Appointment>

预约书类:

import java.util.ArrayList;
import java.util.Collections;

public class AppointmentBook
{
private ArrayList<Appointment> book;

public AppointmentBook()
{
    book = new ArrayList<Appointment>();
}

public void addAppointment(Appointment appt)
{
    book.add(appt);
    Collections.sort(book, new AppointmentComparator());
}

public String printAppointments(int day)
{
    String list = "";

    for (int i = 0; i < book.size(); i++)
    {
        if (book.get(i).getDay() == day)
        {
            list = list + "Appointment description: " + book.get(i).getDescription() + "\n" + "Date of Appointment: " +
            book.get(i).getDay() + "\n" + "Time: " + book.get(i).getStart() + " - " + book.get(i).getEnd() + "\n" + "\n";
        }
    }

    return list;
}

预约课程:

public class Appointment
{
private String desc;
private int day; //in format mmddyyyy
private int start; //in format hhmm
private int end; //in format hhmm

public Appointment(String description, int aptDay, int startTime, int endTime)
{
    desc = description;
    day = aptDay;
    start = startTime;
    end = endTime;
}

public String getDescription()
{
    return desc;
}

public int getDay()
{
    return day;
}

public int getStart()
{
    return start;
}

public int getEnd()
{
    return end;
}

}

Answer 1

从错误消息来看，您似乎忘记将比较器声明为实现接口：

public class AppointmentComparator implements Comparator<Appointment> {}

它需要有实现部分，而不仅仅是包含方法。