Finding duplicate values in arraylist

Question

I have an ArrayList

For Example

class Car{
   String carName;
   int carType;
}

Now, I have to find if the

Answer 1

Create a comparator:

public class CarComparator implements Comparator
{
    public int compare(Car c1, Car c2)
    {
        return c1.carName.compareTo(c2.carName);
    }
}

Now add all the cars of the ArrayList to a SortedSet, preferably TreeSet; if there are duplicates add to the list of duplicates:

List duplicates = new ArrayList();
Set carSet = new TreeSet(new CarComparator());
for(Car c : originalCarList)
{
    if(!carSet.add(c))
    {
        duplicates.add(c);
    }
}

Finally in your duplicates you will have all the duplicates.