Example

Alter Controller to use an ArrayList.  Also demonstrate casting, abstract class.
Please remember to put each class in its own file.
Changes in red.
 

/**
 *
 * @author  default
 */

// must import this class to use it.
import java.util.ArrayList;

// Class controller uses the Vehicle classes.
public class Controller {

    // Default constructor.
    public Controller() {
    }

    // Begin method instantiates two vehicles and passes them to run.
    public void begin() {
        // instantiate our two vehicles.
        Cavalier car1 = new Cavalier(6, 2, 4);
        Hybrid car2 = new Hybrid(50, 8, 4, 5, 68);
 
        // Make an ArrayList to hold our vehicles.  Put them in it.
        ArrayList cars = new ArrayList();
        cars.add(car1);
        cars.add(car2);
        run(cars);

    }

    // run executes the go() method on the vehicle passed in through the ArrayList.
    public void run(ArrayList vehs) {
        // for loop iterates through the ArrayList.
        for (int i = 0; i < vehs.size(); i++) {
            // get the Vehicle out of the ArrayList and cast it from an object to a vehicle.
            Vehicle v = (Vehicle) vehs.get(i);
            // tell it to go 10 units.
            v.go(10);
        }
    }

    // Instantiate and start a Controller object.
    public static void main(String[] args) {
        Controller controller = new Controller();
        controller.begin();
    }

}
 

/*
 * Vehicle.java
 *
 * Created on March 4, 2003, 11:36 PM
 */

/**
 *
 * @author  default
 */
public abstract class Vehicle {
    // Attributes specific to class Vehicle and its subclasses
    protected int gallonsOfGas;
    protected int location;
    protected int mpg;
    protected int miles;
    protected int numberOfTires;

    // Constructor to initialize attributes.
    public Vehicle(int gallonsOfGas, int mpg) {
        this.gallonsOfGas = gallonsOfGas;
        this.mpg = mpg;
    }

    // Go method for Vehicle and its subclasses
    public void go(int distance) {
        location += distance;
        gallonsOfGas = gallonsOfGas - (distance/mpg);
        System.out.println("Travelled " + distance);
        System.out.println("Gallons of Gas remaining: " + gallonsOfGas);
    }
}
 

/*
 * Car.java
 *
 * Created on March 4, 2003, 11:37 PM
 */

/**
 *
 * @author  default
 */
// A subclass of Vehicle

public class Car extends Vehicle {

    // Attributes specific to class Car and its subclasses.
    protected int numberOfDoors;
    protected int numberOfGears;

    // Constructor for Car.
    // Initializes variables and calls constructor for Vehicle.
    public Car(int gallonsOfGas, int numberOfDoors, int numberOfGears, int mpg)
    {
        super(gallonsOfGas, mpg);
        this.numberOfDoors = numberOfDoors;
        this.numberOfGears = numberOfGears;
        numberOfTires = 4;
    }
}
 
 
 

/*
 * Hybrid.java
 *
 * Created on March 4, 2003, 11:39 PM
 */

/**
 *
 * @author  default
 */
// Class Hybrid extends Car
public class Hybrid extends Car {

    // Attributes specific to Hybrid
    protected int kwhRemaining;
    protected int mpkwh;
    protected boolean electricMode;
    protected int minkwh;

    // Constructor for Hybrid.
    // Initializes attributes and calls cosntructor for Car.
    public Hybrid(int kwhRemaining, int gallonsOfGas, int numberOfDoors, int numberOfGears, int mpg) {
        super(gallonsOfGas, numberOfDoors, numberOfGears, mpg);
        this.kwhRemaining = kwhRemaining;
        electricMode = true;
        mpkwh = 2;
    }

    // go() method overrides go() method of Vehicle superclass.
    public void go(int distance) {
        if (electricMode) {
             System.out.println("Travelling via electric mode");
             location += distance;
             kwhRemaining = kwhRemaining - (distance * mpkwh);
             if (kwhRemaining < minkwh) {
                electricMode = false;
             }
             System.out.println("KWH remaining: " + kwhRemaining);
        } else {
            super.go(distance);
        }
    }

    // Method specific to class Hybrid
    public void setElectricMode(boolean electricMode) {
        this.electricMode = electricMode;
    }

    // Method specific to class Hybrid
    public boolean isElectricMode() {
        return electricMode;
    }
}
 
 
 
 

/*
 * Cavalier.java
 *
 * Created on March 4, 2003, 11:38 PM
 */

/**
 *
 * @author  default
 */

// This class extends Car.

public class Cavalier extends Car {
 
    static int cavMpg = 30;
 
    public Cavalier(int gallonsOfGas, int numberOfDoors, int numberOfGears)
    {
        super (gallonsOfGas, numberOfDoors, numberOfGears, cavMpg);
    }

}
 

Results:

Travelled 10
Gallons of Gas remaining: 6
Travelling via electric mode
KWH remaining: 30

 Interfaces