java - 如何将比较器与多个字段对象一起使用？

Question

我尝试使用界面比较器来排序优先队列，以便乘客的顺序首先取决于他们是否有残疾，然后取决于他们拥有的机票类型，最后取决于到达时间。

import java.util.*;

public static void main(String[] args){
    Random rand = new Random(System.nanoTime());
    Comparator<Passenger> comparator;
    PriorityQueue<Passenger> queue = new PriorityQueue<Passenger>(10, comparator);
    Passenger pass[] = new Passenger [10];


    for (int i=0; i<10;i++){
        int time1 = 0;
        pass[i] = new Passenger(rand.nextInt(100000000), rand.nextInt(3) , rand.nextBoolean(), time1);
        time1 = time1 + 15;
    }   

}

在那里我初始化了乘客数组，这是 Passenger 类和比较方法:

public class Passenger implements Comparator<Passenger>{

private int ID;
private int clase;
private boolean disability;
private int arrivalTime;

public Passenger(int ID, int clase, boolean disability, int arrivalTime) {

    this.ID = ID;
    this.clase = clase; // 0-vip 1-economy 2-economy
    this.disability = disability;
    this.arrivalTime = arrivalTime;
}
public int getID() {
    return ID;
}
public void setID(int iD) {
    ID = iD;
}
public int getClase() {
    return clase;
}
public void setClase(int clase) {
    this.clase = clase;
}
public boolean isDisability() {
    return disability;
}
public void setDisability(boolean disability) {
    this.disability = disability;
}
public int getArrivalTime() {
    return arrivalTime;
}
public void setArrivalTime(int arrivalTime) {
    this.arrivalTime = arrivalTime;
}

public int compare(Passenger pas1, Passenger pas2) {
    if((pas1.isDisability()) && (!pas2.isDisability())){
        return 1;                       //passenger 1 has disability
    }else if((!pas1.isDisability()) && (pas2.isDisability())){
        return -1;                          //passenger 2 has disability 
    }
    else{                                   //both have disability or no one has disability 
        if(pas1.getClase() < pas2.getClase()){
            return 1;                   // passenger 1 has better class
        }else if(pas1.getClase() > pas2.getClase()){
            return -1;                      // passenger 2 has better class
        }
        else{                               //both have disability and same class
            if(pas1.getArrivalTime() < pas2.getArrivalTime()){
                return 1;               //passenger 1 arrived before passenger 2
            }
            else return -1;                 //passenger 2 arrived before passenger 1 
        }
    }
}

如何更好地处理这些多级比较？

Answer 1

您的问题似乎是关于简化比较，但我认为您宁愿实现 Comparable<Passenger>而不是Comparator ，并使用#compareTo方法。至于清理，如果您只是抽象实际的 boolean 逻辑，那也有点容易:

public int compareTo(Passenger other) {
    if (this.isDisability() ^ other.isDisability()) { //use an XOR
        return this.isDisability() ? 1 : -1; //1 for us, -1 for other
    }
    //compare #getClase
    int clase = -Integer.compare(this.getClase(), other.getClase()); //invert
    if (clase == 0) {
        //compare arrival times if clase is equal
        //normalize to -1, 1 (0 excluded in OP)
        return this.getArrivalTime() < other.getArrivalTime() ? 1 : -1;
    }
    return clase > 0 ? 1 : -1; //normalize to -1, 0, 1
}

这允许您定义 Passenger 的自然排序。 ，并且被封装/内部到您的类实现中(不需要太多的暴露)。

这也使得排序等操作变得更加容易:

List<Passenger> passengers = /* some list */;
Collections.sort(passengers);

如果您想提供一个可以完成替代排序的比较器，您也可以在您的类中执行此操作:

public class Passenger {

    //...

    public static class ArrivalComparator implements Comparator<Passenger> {

        public int compare(Passenger one, Passenger two) {
            return Integer.compare(one.getArrivalTime(), two.getArrivalTime());
        }
    }

    //...

}

使用我们之前的示例，您可以根据到达时间对所有乘客进行排序:

Collections.sort(passengers, new Passenger.ArrivalComparator());

此外，这可以使用 Java 8 内联:

//Sort by arrival time
Collections.sort(passengers, (one, two) -> Integer.compare(one.getArrivalTime(), two.getArrivalTime());

但总的来说，请记住比较器主要用于定义特定的排序，而 Comparable定义一般/自然顺序。