public class Car{
  String make;
  String model;
  String year;
  String price;
}

Map<String, Car> youCarMap = yourCarList.stream().collect(
                Collectors.toMap(c->c.getMake(), c->c));

Map<String, Car> youCarMap = yourCarList.stream().collect(
                    Collectors.toMap(c->c.getMake(), c->c, (oldValue, newValue) -> oldValue)));

cars.stream()
   .collect(Collectors.toMap(
      car -> car.make,
      Function.identity()
   )