如何在Java中使用Treemap计算对对象

Question

I was trying to have a simple String Pair objects to be counted using a TreeMap.

What I've tried is using this comparator in a treemap, but it still gives me the wrong output as if it compares the pair object to itself:

static class Comp implements Comparator<Pair>
{   
    public int compare(Pair s1, Pair s2)
    {   
        boolean c1 = s1.word1.equals(s2.word1),
               c2 = s1.word2.equals(s2.word2),
               c3 = s1.word1.equals(s2.word2),
               c4 = s1.word2.equals(s2.word1);

        if(c1 && c2 || c3 && c4)
            return 0;   
        else if((!c1 && !c2) || (!c3 && !c4))
            return s1.word1.compareTo(s2.word1);
        if(!c1)
            return s1.word1.compareTo(s2.word1);
        else if(!c2)
            return s1.word2.compareTo(s2.word2);
        else if(!c3)
            return s1.word1.compareTo(s2.word2);
        else if(!c4)
            return s1.word2.compareTo(s2.word1);    
        else
            return s1.word1.compareTo(s2.word1);
    }
}

Example input would be:

<"red", "blue"> , <"blue", "red">, <"red", "red">, <"gray","purple">, <"purple","gray">  

should output:

<"gray", "purple", 2>, <"red", "blue", 2> <"red", "red", 1>

instead i get:

<"gray", "purple", 1><"red", "blue", 2> <"red", "red", 1><"purple", "gray", 1>

Answer 1

I'm not sure how you are coding your counting, but the sorting works as expected with what you've shown of your code. The only difference I've seen between the code below and your code is that the Comp class is not static in mine.

import java.util.Comparator;
import java.util.Map;
import java.util.TreeMap;

public class ComparatorTest {

    public ComparatorTest() {
        Map<Pair, String> x = new TreeMap<>(new Comp());
        x.put(new Pair("red", "blue"), "one");
        x.put(new Pair("blue", "red"), "two");
        x.put(new Pair("red", "red"), "three");
        x.put(new Pair("gray", "purple"), "four");
        x.put(new Pair("purple", "gray"), "five");

        System.out.println(String.format("Print out Map - %s", x.toString()));

        for (Pair pair : x.keySet()) {
            System.out.println(String.format("Key value <%s, %s, %s>", pair.word1, pair.word2, x.get(pair)));
        }
    }

    public static void main(String[] args) {
        new ComparatorTest();
    }
}

class Pair {
    String word1 = null;
    String word2 = null;

    public Pair(String word1, String word2) {
        this.word1 = word1;
        this.word2 = word2;
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Pair)) { return false; }

        Pair that = (Pair)obj;

        return ((this.word1.equals(that.word1) && this.word2.equals(that.word2)) || (this.word1.equals(that.word2) && this.word2.equals(that.word1)));
    }

    @Override
    public String toString() {
        return String.format("<%s, %s>", word1, word2);
    }
}

class Comp implements Comparator<Pair> {   
    public int compare(Pair s1, Pair s2) {   
        boolean c1 = s1.word1.equals(s2.word1),
               c2 = s1.word2.equals(s2.word2),
               c3 = s1.word1.equals(s2.word2),
               c4 = s1.word2.equals(s2.word1);

        if(c1 && c2 || c3 && c4)
            return 0;   
        else if((!c1 && !c2) || (!c3 && !c4))
            return s1.word1.compareTo(s2.word1);
        if(!c1)
            return s1.word1.compareTo(s2.word1);
        else if(!c2)
            return s1.word2.compareTo(s2.word2);
        else if(!c3)
            return s1.word1.compareTo(s2.word2);
        else if(!c4)
            return s1.word2.compareTo(s2.word1);    
        else
            return s1.word1.compareTo(s2.word1);
    }
}

Output

Print out Map - {<gray, purple>=five, <red, blue>=two, <red, red>=three}
Key value <gray, purple, five>
Key value <red, blue, two>
Key value <red, red, three>