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.
Please add two methods to the RemoteControlCar
interface:
drive()
, returning nothing, andgetDistanceTravelled()
, returning an int
.Then make ProductionRemoteControlCar
and ExperimentalRemoteControlCar
implement the RemoteControlCar
interface.
This includes implementing all methods required by the interface.
Each call of .drive()
should make the car travel a certain distance:
ProductionRemoteControlCar
drives 10 units,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();
prod.drive();
prod.getDistanceTravelled();
// => 10
ExperimentalRemoteControlCar exp = new ExperimentalRemoteControlCar();
exp.drive();
exp.getDistanceTravelled();
// => 20
Implement the TestTrack.race(RemoteControlCar car)
method in which the car
s get to drive()
.
TestTrack.race(new ProductionRemoteControlCar());
TestTrack.race(new ExperimentalRemoteControlCar());
// this should execute without an exception being thrown
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();
prc1.setNumberOfVictories(2);
prc2.setNumberOfVictories(3);
List<ProductionRemoteControlCar> unsortedCars = new ArrayList<>();
unsortedCars.add(prc1);
unsortedCars.add(prc2);
List<ProductionRemoteControlCar> rankings = TestTrack.getRankedCars(unsortedCars);
// => rankings.get(0) == prc2
// => rankings.get(1) == prc1
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