public interface Vehicle {
   public double getVehicleWeight();
}

public class Car implements Vehicle{
    private final long carWeight;

    //constructor here...

    @Override
    public double getVehicleWeight() {
        return this.carWeight;
    }

}

TreeMap<String,Vehicle> vehicles = new TreeMap<String,Vehicle>();
vehicles.put("AXK-KF1",new Car(...));
System.out.println(vehicles.get("AXK-KF1").getVehicleWeight());