如何在Java中定義基於兩個變量進行比較的Comparator

Question

我想創建一個比較器進行操作，使得到達時間較短的進程首先出現在排序中，如果兩個進程具有相同的到達時間，那么具有較低進程ID的進程將首先排序。 我嘗試了以下代碼，但它似乎沒有工作。 有沒有人看到它的缺陷？

public class FCFSComparator implements Comparator<Process>
{
    public int compare(Process o1, Process o2)
    {
        int result = o1.getArrivalTime() - o2.getArrivalTime();

        if(result == 0)
        {
            return (o1.getPid() < o2.getPid()) ? -1 : 1;
        }
        else
        {
            return result;
        }
//        return (result != 0 ? result : o1.getPid() - o2.getPid());
    }
}

具體而言，給出如下過程

pid = 0 arrival time = 10
pid = 1 arrival time = 30
pid = 2 arrival time = 15
pid = 3 arrival time = 15
pid = 4 arrival time = 66

我最后得到以下訂購

Pid = 0 arrival time = 10
Pid = 2 arrival time = 15
Pid = 1 arrival time = 30
Pid = 4 arrival time = 66
Pid = 3 arrival time = 15

Answer 1

我發現你的比較器沒有任何問題。 這是我的測試用例：

public class TestComparator {

    static class Process {
        int pid;
        int arrivalTime;

        Process(int pid, int arrivalTime) {
            this.pid = pid;
            this.arrivalTime = arrivalTime;
        }

        @Override
        public String toString() {
            return "Process [pid=" + pid + ", arrivalTime=" + arrivalTime + "]";
        }
    }

    static class FCFSComparator implements Comparator<Process> {
        public int compare(Process o1, Process o2) {
            int result = o1.arrivalTime - o2.arrivalTime;

            if (result == 0) {
                return (o1.pid < o2.pid) ? -1 : 1;
            } else {
                return result;
            }
        }
    }

    public static void main(String[] args) {
        List<Process> processes = Arrays.asList(
                new Process(0, 10),
                new Process(1, 30),
                new Process(2, 15),
                new Process(3, 15),
                new Process(4, 66));

        Collections.sort(processes, new FCFSComparator());

        for (Process process : processes) {
            System.out.println(process);
        }

    }
}

輸出：

Process [pid=0, arrivalTime=10]
Process [pid=2, arrivalTime=15]
Process [pid=3, arrivalTime=15]
Process [pid=1, arrivalTime=30]
Process [pid=4, arrivalTime=66]

Answer 2

我假設你比較的東西都是int 。 在兩個變量相等的情況下，您仍然從內部比較返回1。 這樣的事情應該有所幫助：

public class FCFSComparator implements Comparator<Process>
{
    public int compare(Process o1, Process o2)
    {
        int result = o1.getArrivalTime() - o2.getArrivalTime();
        if (result == 0)
        {
            return o1.getPid() - o2.getPid();
        }
        else
        {
            return result;
        }
    }
}

編輯：我檢查了上面的代碼，它確實輸出了正確的順序。 我只能假設你的代碼中的其他地方有一個bug。

Pid = 0 arrival time = 10
Pid = 2 arrival time = 15
Pid = 3 arrival time = 15
Pid = 1 arrival time = 30
Pid = 4 arrival time = 66

完整的測試代碼是：

import java.util.Comparator;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;

public class Main
{
    public static void main(String[] args)
    {
        List<Process> processes = new ArrayList<Process>();
        processes.add(new Process(10, 0));
        processes.add(new Process(30, 1));
        processes.add(new Process(15, 2));
        processes.add(new Process(15, 3));
        processes.add(new Process(66, 4));

        Collections.sort(processes, new FCFSComparator());

        for (Process process : processes)
            System.out.println("Pid = " + process.getPid() + " arrival time = " + process.getArrivalTime());
    }

    static class FCFSComparator implements Comparator<Process>
    {
        public int compare(Process o1, Process o2)
        {
            int result = o1.getArrivalTime() - o2.getArrivalTime();
            if (result == 0)
            {
                return o1.getPid() - o2.getPid();
            }
            else
            {
                return result;
            }
        }
    }

    static class Process
    {
        private int arrivalTime;
        private int pid;

        Process(int arrivalTime, int pid)
        {
            this.arrivalTime = arrivalTime;
            this.pid = pid;
        }

        public int getArrivalTime()
        {
            return arrivalTime;
        }

        public int getPid()
        {
            return pid;
        }
    }
}

Answer 3

我相信你想要這個：

public class FCFSComparator implements Comparator<Process> {
    public int compare(Process o1, Process o2) {
        if (o1.getArrivalTime() == o2.getArrivalTime()) {
            return (o1.getPid() < o2.getPid()) ? -1 : 1;
        }
        return (o1.getArrivalTime() < o2.getArrivalTime()) ? -1 : 1;
    }
}

Answer 4

最簡單的是：

public class FCFSComparator implements Comparator<Process>
{
    public int compare(Process o1, Process o2)
    {
        int timeCmp = Integer.valueOf(o1.getArrivalTime()).compareTo(Integer.valueOf(o2.getArrivalTime()));
        return (timeCmp != 0 ? timeCmp : Integer.valueOf(o1.getPid()).compareTo(Integer.valueOf(o2.getPid())));
    }
}