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

Try this:

List cars = getCars();
Set names = new HashSet();
for (Car car:cars) {
  if (names.contains(car.getName()) {
    duplicate(car);   // some magic handler
  } else {
    names.add(car.getName());
  }
}

Note: this will give you the car names that are duplicate. A follow on would be extracting all cars with those names from the list (if you need the Car objects)