具有 2 个优先级参数的 Java 优先级队列

Question

我有一个 Person 类，它实现了 Comparable，如下所示，因为我想将 Person 的对象放入优先级队列中。

public class Student implements Comparable{
    private String fullName;
    private Date registrationDate;

public Person(String fullName){
    this.fullName = fullName;
}

public String getFullName() {
    return fullName;
}

public void setFullName(String fullName) {
    this.fullName = fullName;
}

public Date getRegistrationDate() {
        return registrationDate;
    }
    public void setRegistrationDate(Date registrationDate) {
        this.registrationDate = registrationDate;
    }

@Override
    public int compareTo(Object obj) {
        Person person = (Person) obj;

        if(person instanceof Staff){
            return 1; 
        }else if(person instanceof Student){
            return -1;
        }
        else if(getRegistrationDate().before(person.getRegistrationDate())){
            return 1;
        }else if(getRegistrationDate().after(person.getRegistrationDate())){
            return -1;
        }
        return 0;
    }
}

我有两个扩展 Person 的类，如下所示

public class Staff extends Person{
    public Staff(String fullName){
        this.fullName = fullName;
     }
}

public class Student extends Member{
    public Student(String fullName){
        this.fullName = fullName;
     }
}

在主方法中，我创建了 Staff 对象和 Students 对象，设置对象的注册日期并将它们放入优先级队列中

public class School {

    public static void main(String args[]) {

        //list of students
        Student student1 = new Student("John Kent");
        Date dateStudent1Joined = new GregorianCalendar(2014, Calendar.JULY, 1).getTime();
        student1.setRegistrationDate(dateStudent1Joined);

        Student student2 = new Student("Peter Tush");
        Date dateStudent2Joined = new GregorianCalendar(2014, Calendar.JULY, 2).getTime();
        student2.setRegistrationDate(dateStudent2Joined);

        Student student3 = new Student("Mike Monroe");
        Date dateStudent3Joined = new GregorianCalendar(2014, Calendar.JULY, 3).getTime();
        student3.setRegistrationDate(dateStudent3Joined);

        Student student4 = new Student("Tom Johnson");
        Date dateStudent4Joined = new GregorianCalendar(2014, Calendar.JULY, 4).getTime();
        student4.setRegistrationDate(dateStudent4Joined);

        Student student5 = new Student("Tony Spencer");
        Date dateStudent5Joined = new GregorianCalendar(2014, Calendar.JULY, 5).getTime();
        student5.setRegistrationDate(dateStudent5Joined);

        //list of staff
        Staff staff1 = new Staff("Luke Clint");
        Date dateStaff1Joined = new GregorianCalendar(2014, Calendar.JULY, 6).getTime();
        staff1.setRegistrationDate(dateStaff1Joined);

        Staff staff2 = new Staff("Ron West");
        Date dateStaff2Joined = new GregorianCalendar(2014, Calendar.JULY, 7).getTime();
        staff2.setRegistrationDate(dateStaff2Joined);

        Staff staff3 = new Staff("Jim Gary");
        Date dateStaff3Joined = new GregorianCalendar(2014, Calendar.JULY, 8).getTime();
        staff3.setRegistrationDate(dateStaff3Joined);


        //create a queue data structure to hold Persons in school
        PriorityQueue<Person> schoolQueue = new PriorityQueue<Person>();
        //add students to queue
        schoolQueue.offer(student1);
        schoolQueue.offer(student2);
        schoolQueue.offer(student3);
        schoolQueue.offer(student4);
        schoolQueue.offer(student5);
        //add staff to queue
        schoolQueue.offer(staff1);
        schoolQueue.offer(staff2);
        schoolQueue.offer(staff3);

        //print names of people in queue
        for(Member member : clubQueue){
            String memberName = member.getFullName();
            System.out.println(memberName);
        }

    }
}

我的优先级队列应遵循 3 条规则1.教职员对象的优先级应高于学生对象2.报到日期早的人员优先于报到时间晚的人员3.报到时间早的学生优先于报到时间晚的学生。

我得到的输出目前没有产生预期的结果。教职员工对象的优先级高于学生对象，但根据日期的优先级不起作用。我知道compareTo方法中的规则是问题所在，我该如何改进它？为了方便起见，又是这样

@Override
        public int compareTo(Object obj) {
            Person person = (Person) obj;

            if(person instanceof Staff){
                return 1; 
            }else if(person instanceof Student){
                return -1;
            }
            else if(getRegistrationDate().before(person.getRegistrationDate())){
                return 1;
            }else if(getRegistrationDate().after(person.getRegistrationDate())){
                return -1;
            }
            return 0;
        }

Answer 1

让我们首先让您的 Person 类使用泛型类型而不是原始类型:

public class Person extends Comparable<Person>

然后让我们为类分配优先级。您没有告诉“裸”人(既不是教职员工也不是学生)应该如何与其他人进行比较。因此，我假设“裸”人不应该存在，并且您的 Person 类应该是抽象的:

public abstract class Person extends Comparable<Person>

然后您希望每个类别都有一个优先级。因此，让我们实现它，而不是依赖丑陋的 instanceof:

protected abstract int getPriority();

员工应该出现在学生之前，因此在员工中:

@Override
protected int getPriority() {
    return 0;
}

在学生中:

@Override
protected int getPriority() {
    return 1000;
}

现在让我们实现compareTo方法:

public int compareTo(Person other) {
    int result = Integer.compare(this.getPriority(), other.getPriority());
    if (result == 0) {
        result = this.getRegistrationDate().compareTo(other.getRegistrationDate())
    }
    return result;
}

请注意，添加另一种 Person 是微不足道的。您只需在 getPriority 中返回适当的值即可，比较代码无需更改。

另请注意，compareTo 现在采用 Person 作为参数，并且由于通用类型正确，编译器现在将阻止您执行诸如 person.compareTo("foo") 之类的愚蠢操作。

如果使用 Java 8，您的compareTo 方法可能会更简单:

private static final Comparator<Person> COMPARATOR = 
    Comparator.comparingInt(Person::getPriority) 
              .thenComparing(Person::getRegistrationDate);

@Override
public int compareTo(Person other) {
    return COMPARATOR.compare(this, other);
}