Java TreeMap 未根据通过的比较器排序

Question

I have implemented a TreeMap that contains blueprints (to simplify it).

private TreeMap<BuildingFloorKey, Blueprint> blueprints = new TreeMap<>((o1, o2) -> {
        int value = o1.compareTo(o2);
        return value;
});

To use building (in my case called complex) and floor as a tuple key, I wrote the following class:

public static class BuildingFloorKey {
    private Complex mComplex;
    private int mFloor;

    public BuildingFloorKey(Complex complex, int floor){
        mComplex = complex;
        mFloor = floor;
    }

    @Override
    public boolean equals(Object other) {
        if (!(other instanceof BuildingFloorKey)) return false;
        BuildingFloorKey that = (BuildingFloorKey) other;
        return mFloor == that.mFloor && mComplex.equals(that.mComplex);
    }

    @Override
    public int hashCode() {
        return Arrays.hashCode(new Object[]{mComplex, mFloor});
    }

    public int compareTo(BuildingFloorKey otherKey){
        if(this.equals(otherKey)) return 0;

        //same complex -> compare floors
        else if (this.getComplex().equals(otherKey.getComplex())){
            return otherKey.getFloorInt() - this.getFloorInt();
        }
        //different complexes (incl. some modification for special cases)
        else return -(Math.abs(otherKey.mFloor + 2) + 100);
    }
}

I am working on an Android App and I want to click through the blueprints via buttons. For that I make use of the methods TreeMap.lowerKey(otherKey) and TreeMap.higherKey(otherKey). Like so:

@Override
    public void onNextPlanClicked() {
           nextFloorPlan = blueprints.higherKey(currentlyDisplayedPlan);
           drawFloorPlan(nextFloorPlan);
        }

As an example, I have a usecase where the set of blueprints is

• 04|02
• 03|03
• 04|-1
• 03|00

(format: complex|floor). Unfortunately, it is not sorted properly in the TreeMap (as you can see - the list above is sorted like the entries of the TreeMap in the debugger).

I read something about TreeMap Sorting using case-sensitive Strings. But I'm actually using integers. So I don't get why sorting and using lowerKey() and higherKey() not working properly. Did I mess up with the comparator? Can someone help please?

Answer 1

I think your issues is a very simple one, your compareTo method should have an override. You need to add implements Comparable to your BuildingFloorKey definition, which will then take your compareTo argument as a comparable that TreeMap can recognize.