Question

I have 3 different TreeSet objects in my application, all of which store the same class of object.

However, at any one point of time, a single object may exist in only one of the TreeSets.

So, if I queried each TreeSet using contains() for a particular object it should exist in only one of them.

Is there an easy way to add this kind of logic to my TreeSet easily? Obviously I can perform the above contains() check myself after each operation but just wondering if there are better ways?

Thanks

Answer 1

You can keep a map that maps objects to the TreeSet to which they currently belong. If an object has no entry, it can be added to a TreeSet; otherwise it must be removed from the mapped TreeSet before it assigned to a new one.

EDIT:

Per your request, here’s a code snippet for how this might be done:

Map<MyObject, TreeSet<MyObject>> map = new HashMap<MyObject, TreeSet<MyObject>>();

void addToSet(MyObject obj, TreeSet<MyObject> set) {
    TreeSet<MyObject> otherSet = map.get(obj);
    if (otherSet != null) {
        otherSet.remove(obj);
    }
    set.add(obj);
    map.put(obj, set);
}

void removeFromSet(MyObject obj, TreeSet<MyObject> set) {
    set.remove(obj);
    map.remove(obj);
}