Java TreeMap malfunctioning

Question

I have a TreeMap:

final Map<UserSetting, ItemsIntersectionAndComplement> _usersSimilar = new TreeMap<UserSetting, ItemsIntersectionAndComplement>(new Comparator<UserSetting>() {

@Override
public int compare(UserSetting lhs, UserSetting rhs) {

int prec = (lhs.id()).compareTo(rhs.id());
return lhs.totalMatch > rhs.totalMatch ? -1 : (lhs.totalMatch < rhs.totalMatch ) ? 1 : prec;
}
});

And when checking wether key exist, it respond false, but at a specific nth position I see that item. How is it possible? And in previous iteration item was added.

if (!_usersSimilar.containsKey(rating2.userSetting())) { // <-- CHECKING HERE EXISTENCE

    ItemsIntersectionAndComplement iiac = new ItemsIntersectionAndComplement();
    iiac.intersection.add(rating2.item());
    rating2.userSetting().totalMatch = 1;
    _usersSimilar.put(rating2.userSetting(), iiac);
} else {
  //.. SOME CODE, BUT CALL DOES NOT REACH IT
}

public class UserSetting extends _UserSetting {
    public UserSetting() {
    }

    int totalMatch;
}

Answer 1

Eran is right in his answer above. Your TreeMap is broken because you are updating totalMatch. This code reproduces the problem.

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

public class HashMapWithComparatorTest {
    public static void main(String[] args) {
        final Map<UserSetting, String> _usersSimilar = new TreeMap<UserSetting, String>(new Comparator<UserSetting>() {

            @Override
            public int compare(UserSetting lhs, UserSetting rhs) {

                int prec = (lhs.id()).compareTo(rhs.id());
                return lhs.totalMatch > rhs.totalMatch ? -1 : (lhs.totalMatch < rhs.totalMatch ) ? 1 : prec;
            }
        });

        UserSetting setting1 = new UserSetting(2, 1);
        UserSetting setting2 = new UserSetting(3, 1);
        UserSetting setting3 = new UserSetting(1, 1);
        UserSetting setting4 = new UserSetting(1, 1);
        UserSetting setting5 = new UserSetting(2, 2);

        _usersSimilar.put(setting1, "test");
        _usersSimilar.put(setting2, "test");
        _usersSimilar.put(setting3, "test");
        _usersSimilar.put(setting4, "test");


        System.out.println("Before touching totalMatch:");
        System.out.println(_usersSimilar.containsKey(setting1));
        System.out.println(_usersSimilar.containsKey(setting2));
        System.out.println(_usersSimilar.containsKey(setting3));
        System.out.println(_usersSimilar.containsKey(setting4));
        System.out.println(_usersSimilar.containsKey(setting5));

        setting1.totalMatch++;
        setting1.totalMatch++;

        setting2.totalMatch--;
        setting2.totalMatch--;

        setting3.totalMatch++;
        setting3.totalMatch++;

        setting4.totalMatch--;
        setting4.totalMatch--;

        setting5.totalMatch++;
        setting5.totalMatch++;

        System.out.println("After changing totalMatch:");
        System.out.println(_usersSimilar.containsKey(setting1));
        System.out.println(_usersSimilar.containsKey(setting2));
        System.out.println(_usersSimilar.containsKey(setting3));
        System.out.println(_usersSimilar.containsKey(setting4));
        System.out.println(_usersSimilar.containsKey(setting5));
    }

    private static class UserSetting {
        private int id;
        public int totalMatch;

        public Integer id() {
            return id;
        }

        public UserSetting(int id, int totalMatch) {
            this.id = id;
            this.totalMatch = totalMatch;
        }
    }
}

Answer 2

if (!_usersSimilar.containsKey(rating2.userSetting())) { // <-- CHECKING HERE EXISTENCE

    ItemsIntersectionAndComplement iiac = new ItemsIntersectionAndComplement();
    iiac.intersection.add(rating2.item());
    rating2.userSetting().totalMatch = 1;
    _usersSimilar.put(rating2.userSetting(), iiac);
}

The key you are searching for in the Map and the key you put in the Map have different state, since you are updating rating2.userSetting().totalMatch inside your if clause.

Therefore it's quite possible the key you are searching for doesn't exist in the Map but the key you are adding exists in the Map.

Answer 3

In the Javadoc for TreeMap, you read:

Note that the ordering maintained by a tree map, like any sorted map, and whether or not an explicit comparator is provided, must be consistent with equals if this sorted map is to correctly implement the Map interface.

Since you have not overridden equals, in your case the comparator is not consistent with equals. You have to equip your UserSetting class with an equals method, for example:

public boolean equals(Object o) {
    if (this == o) {
        return true;
    }
    if (!(o instanceof UserSetting)) {
        return false;
    }
    UserSetting s = (UserSetting)o;
    return id == s.id && totalMatch = s.totalMatch;
}