Question

Implement the ArrayQueue class

In the ‘Queues’ lecture, review the ‘Introduce next lab’ section.  See here that we can use a circular array to implement the queue data structure.  You must write a class named ArrayQueue that does this.

ArrayQueue will be a generic class, that implements our generic QueueInterface interface.  This demonstrates the Java interface feature, where we have already implemented queue dynamically, using the LinkedQueue class covered during the lecture.

Many classes are given to you

Download and unzip the Circular array project from Canvas, ‘Queues’ module, Example programs.  Open the project in BlueJ and see Tester::main().  This shows the methods you have to implement.  You must write your code in the ArrayQueue class, that implements the circular array.  In ArrayQueue, you must use only the instance variables given to you, you are not allowed to add more.  Other than adding your new methods to ArrayQueue, and adding a new QueueOverflowException class, the code provided must not be altered in any way.

Hints

Note that the array implementation does not require our Item class.  Instead the array contains elements of the generic data type T.

The syntax in the ArrayQueue constructor to create an array of the generic data type T is awkward, so has been given to you.  See how the code creates an array of Object, which is then typecast to data type T.  Cool!  Also, see here how I’ve changed the usual initializations of front and rear, because I want to force wrapping to happen early.

Queue overflow was not a problem for our previous linked list implementation, but is obviously a problem for an array implementation.  So you will have to add a new QueueOverflowException class.

Run the program to test your completed ArrayQueue class.  When correct, save the output as an output.txt text file, saved in the BlueJ project folder.

Required

Your program must be correct, simple and clear:

• clear, consistent layout and indentation

• you must Javadoc comment every class, method and anything that is not simple and clear. (‘How to write Javadoc comments’ has been added to Course information)

• clear, meaningful variable and method names

Given Code

public class ArrayQueue<T> implements QueueInterface<T>

{

    public static final int MAX = 10;

    //use only these 3 instance variables!

    //you are NOT ALLOWED to add more instance variables

    private T elements[];

    private int front;

    private int rear;

    public ArrayQueue()

    {

        //awkward syntax!

        elements = (T[]) new Object[MAX];

        /* the usual initialisations

        front = MAX - 1;

        rear = MAX - 1;

        */

        //tweaked here to deliberately force early wrapping!

        front = MAX - 3;

        rear = MAX - 3;

    }

    

    //implement your methods with Javadoc comments here

    //again, you are NOT ALLOWED to add more instance variables

    

}

public class Item<T>

{

    protected T info;

    protected Item<T> next;

    public Item()

    {

        info = null;

        next = null;

    }

    public Item(T info)

    {

        this.info = info;

        next = null;

    }

}

public interface QueueInterface<T>

{

    void insert(T element);

    T remove() throws QueueUnderflowException;

    Boolean isEmpty();

}

public class QueueOverflowException extends RuntimeException

{

    public QueueOverflowException(){

        super();

    }

    

    public QueueOverflowException(String message){

        super(message);

    }

}

public class QueueUnderflowException extends RuntimeException

{

    public QueueUnderflowException()

    {

        super();    

    }

    public QueueUnderflowException(String message)

    {

        super(message);    

    }

}

public class Tester

{

    public static void main()

    {

        QueueInterface<Character> q = new ArrayQueue<Character>();

        //insert into the queue, with wrapping

        for (Character ch = 'a'; ch <= 'h'; ++ch)

            q.insert(ch);

        //remove the first 5 items, with wrapping

        for (int i = 1; i <= 5; ++i)

            System.out.print(q.remove());

        System.out.println();

        //now fill the queue

        for (Character ch = 'A'; ch <= 'F'; ++ch)

            q.insert(ch);

        //test the new QueueOverflow exception

        try {

            q.insert('!');

        }

        catch (QueueOverflowException overflow) {

        System.out.println("Exception: " + overflow.getMessage());

        System.err.println("Exception: " + overflow.getMessage());

        //System.exit(2);

        }

        //empty the queue

        while (!q.isEmpty())

            System.out.print(q.remove());

        System.out.println();

        System.out.println("done");

    }

}