Question

I am doing the following

class RuleObject implements Comparable{



    @Override
    public String toString() {
        return "RuleObject [colIndex=" + colIndex + ", probability="
                + probability + ", rowIndex=" + rowIndex + ", rule=" + rule
                + "]";
    }
    String rule;
    double probability;
    int rowIndex;

    int colIndex;

    public RuleObject(String rule, double probability) {
        this.rule = rule;
        this.probability = probability;
    }
    @Override
    public int compareTo(Object o) {

        RuleObject ruleObj = (RuleObject)o;
        System.out.println(ruleObj);
        System.out.println("---------------");
        System.out.println(this);
        if(ruleObj.probability > probability)
            return 1;
        else if(ruleObj.probability < probability)
            return -1;
        else{
            if(ruleObj.colIndex == this.colIndex && ruleObj.rowIndex == this.rowIndex && ruleObj.probability == this.probability && ruleObj.rule.equals(this.rule))
                return 0;
        }
        return 1;

    }


}

And I have a TreeSet containing elements of RuleObject.
I am trying to do the following :

System.out.println(sortedHeap.size());
        RuleObject ruleObj = sortedHeap.first();
        sortedHeap.remove(ruleObj);
System.out.println(sortedHeap.size());

I can see that the size of set remains same. I am not able to understand why is it not being deleted.
Also while deleting I could see compareTo method is called. But it is called for only 3 object whereas in set there are 8 objects.
Thanks

Answer 1

Look at the specification for remove:

Removes the specified element from this set if it is present. More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if this set contains such an element.

Your problem is that RuleObject does not @Override equals(Object other). You need to do that, and of course, with that you also need to @Override hashCode().

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Also, the reason why compareTo is being called fewer times than the number of elements is because it’s supposed to be a O(log N) operation; that’s the whole purpose of using TreeSet. If you have 1024 elements, you can expect compareTo to be called no more than 10 times.

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As Vlad points out, your comparator is broken. Specifically, the last statement return 1; breaks it. You should expand the equal probability case to return -1, 0, +1 depending on the other fields.