Question

With solid C++ in my back some Java concepts are not 100% clear.

List<SomeInterface> list = new ArrayList<SomeImplementation>; 

This is 100% clear needs no explanation – but it has consequences…

interface Drivable {...}
class Car implements Drivable  {...}
class Bike implements Drivable  {...}
class Skateboard implements Drivable  {...}

class MyGarage{
List<Driveable> myRides;

public void addRides( List<Driveable> rideList ){...} 

Is not callable with List<Car>. However I can add Cars to myRides by:

public void addCars( List<Car> carList ){
myRides.addAll( new List<Driveable>( carList ) );

Q1: Is this a good idea?

I would really want something like the first function to work. By doing something that corresponds to C++ const& and adding a copy of the incoming carList to myRides I am thinking carList would be protected from illegal access. My hopes of adding final as a function argument were crushed.

Q2: Is there some way to make a fully callable addRides(List<Driveable> rideList) work?

Nor is overloading ( List<Car> List<Bike> etc ) legal.

And yes I can make this work by adding separate functions addBikes() addCars etc or I could do new List<Drivable> at each point of call. But I am hoping for something sleeker.

Q3: Any suggestions?

Thanks a lot!
Adam

Answer 1

Your addRides method should be like this:

public void addRides(Collection<? extends Drivable> c)

When in doubt about generics usage, look for the collection interfaces in java.util, they have lots of examples, what you want to do is the same as what Collection.addAll() does.