Finding duplicate values in arraylist

by

Create a comparator:

public class CarComparator implements Comparator<Car>
{
    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<Car> duplicates = new ArrayList<Car>();
Set<Car> carSet = new TreeSet<Car>(new CarComparator());
for(Car c : originalCarList)
{
    if(!carSet.add(c))
    {
        duplicates.add(c);
    }
}

Finally in your duplicates you will have all the duplicates.

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