Remote Control Competition
Remote Control Competition

Remote Control Competition

Learning Exercise



An interface is a type containing members defining a group of related functionality. It distances the uses of a class from the implementation allowing multiple different implementations or support for some generic behavior such as formatting, comparison or conversion.

The syntax of an interface is similar to that of a class except that methods appear as the signature only and no body is provided.

public interface Language {
    String getLanguageName();
    String speak();

public class ItalianTraveller implements Language, Cloneable {

    // from Language interface
    public String getLanguageName() {
        return "Italiano";

    // from Language interface
    public String speak() {
        return "Ciao mondo";

    // from Cloneable interface
    public Object clone() {
        ItalianTraveller it = new ItalianTraveller();
        return it;

All operations defined by the interface must be implemented by the implementing class.

Interfaces usually contain instance methods.

An example of an interface found in the Java Class Library, apart from Cloneable illustrated above, is Comparable<T>. The Comparable<T> interface can be implemented where a default generic sort order in collections is required.


In this exercise you will be doing some more work on remote control cars.

An experimental car has been developed and the test track needs to be adapted to handle both production and experimental models. The two types of car have already been built and you need to find a way to deal with them both on the test track.

In addition, production cars are beginning to have some success. The team boss is keen to maintain the competitive spirit by publishing a ranking of the production cars.

1. Implement the Interface

Please add two methods to the RemoteControlCar interface:

  • drive(), returning nothing, and
  • getDistanceTravelled(), returning an int.

Then make ProductionRemoteControlCar and ExperimentalRemoteControlCar implement the RemoteControlCar interface. This includes implementing all methods required by the interface.

2. Drive

Each call of .drive() should make the car travel a certain distance:

  • a ProductionRemoteControlCar drives 10 units,
  • an ExperimentalRemoteControlCar drives 20 units.

The .getDistanceTravelled() method should return the number of units that the car has travelled in its lifetime.

ProductionRemoteControlCar prod = new ProductionRemoteControlCar();;
// => 10
ExperimentalRemoteControlCar exp = new ExperimentalRemoteControlCar();;
// => 20

3. Race

Implement the TestTrack.race(RemoteControlCar car) method in which the cars get to drive().

TestTrack.race(new ProductionRemoteControlCar());
TestTrack.race(new ExperimentalRemoteControlCar());
// this should execute without an exception being thrown

4. Allow the production cars to be sorted

Please implement the Comparable<T> interface in the ProductionRemoteControlCar class. The default sort order for cars should be descending order of victories.

Implement the static TestTrack.getRankedCars() to return the cars passed in, sorted in descending order of number of victories.

ProductionRemoteControlCar prc1 = new ProductionRemoteControlCar();
ProductionRemoteControlCar prc2 = new ProductionRemoteControlCar();
List<ProductionRemoteControlCar> unsortedCars = new ArrayList<>();
List<ProductionRemoteControlCar> rankings = TestTrack.getRankedCars(unsortedCars);
// => rankings.get(0) == prc2
// => rankings.get(1) == prc1
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