Compare two arraylist of different types

Question

I have 2 array-list called assignment and person and both of different type and different sizes also. Problem statement :I wanna remove items from person where person id equals assignment id, i hv written following Comparator.

SortedSet<Map.Entry<AssignmentResults, Person>> text = new TreeSet<Map.Entry<AssignmentResults, Person>>(
        new Comparator<Map.Entry<AssignmentResults, Person>>() {

            @Override
            public int compare(Entry<AssignmentResults, Person> lhs,
                    Entry<AssignmentResults, Person> rhs) {
                // TODO Auto-generated method stub
                int statusvalue = 0;

                if (rhs.getValue().getId()
                        .equals(lhs.getKey().getId()))
                    statusvalue = 1;

                return statusvalue;
            }

        });

But im not sure how to use this to get person arraylist where all item which does not contains assignment id will be removed.plz any help will be appreciated. I need logic which is robust with less complexity

Answer 1

You can save all assigments' ids to HashSet and then remove items from list of persons with for-loop :

Set<Long> assigmentsIdsSet = new HashSet<Long>(); // here we will store all assigments' ids

for (AssignmentResults assigment : assigmentsList) { // assigmentsList is your array list of assigments
    assigmentsIdsSet.add(assigment.getId());
}

// now go through list of persons and remove persons with ids from assigmentsIdsSet
for (Iterator<Person> it = personList.iterator(); it.hasNext(); ) {
    if (assigmentsIdsSet.contains(it.next().getId())) {
        it.remove();
    }
}

1. There is no way how the code above could throw an ArrayOutOfBounds exception
2. It has linear complexity on the size of arrays

Answer 2

It's confusing: you intend to work on lists and you compare map entries.

You could just:

• Have your Person and Assignment classes both implement a common interface with getId .

• Overide equals in both classes so that objects with the same id are equal. You would cast Object parameters to instances of your common interface with getId .

• You should also overide hashCode so that objects with the same id have the same hashcode. You could just return getId().getHashCode() if id is an object.

• You can then do persons.removeAll(assignments)

As a side note, all of this is not really "clean"; but it would get the job done for that specific use case. Just don't rely on this if you intend to provide a library with many other use cases