Question

How do I implement
public class CircularArrayQueue<E> extends AbstractQueue <E> and test the methods with junit?

Answer 1

Well I have created the code for you. For an implementation of queues based on arrays. The head of the queue starts out at the head of the array, allowing the queue to grow and shrink in constant time. This queue implementation is ideal for applications that require a queue with a known maximum size that expands in constant time.

Here's the code for implementation public class CircularArrayQueue<E> extends AbstractQueue <E> and the methods with junit

import java.util.NoSuchElementException;

public class CircularArrayQueue implements MyQueue 
{
private Integer[] array;
//initial size of the array
private int N;
private int front;
private int rear;
private int count = 0;//total number of items currently in queue.
public CircularArrayQueue()
{
    this.N = 10;
    array = new Integer[N];
    front = rear = 0;
}

public CircularArrayQueue(int size)
{
    this.N = size;
    array = new Integer[N];
    front = rear = 0;
}


//enqueues an element at the rear of the queue
// if the queue is already full it is resized, doubling its size
@Override
public void enqueue(int in) 
{
    count++;
    if (isFull())
    {
       resize();
       rear = (rear + 1) % N;
       array[rear] = in;
    }
    else
    {
       rear = (rear + 1) % N;
       array[rear] = in;
    }            
}

public void resize()
{
    Integer[] temp = new Integer[array.length*2];
    N = array.length*2;
    for(int i=0; i<array.length; i++)
    {
        temp[i] = array[i];
    }

    array = temp;
}


//dequeues an element
// if the queue is empty a NoSuchElement Exception is thrown
@Override
public int dequeue() throws NoSuchElementException 
{
    if(isEmpty())
    {
        throw new Exception("The queue is empty");
    }

    front = (front + 1) % N;
    int headElement = array[front];   
    count--;
    return headElement;
}

@Override
public int noItems() 
{   
    return count;
}

@Override
public boolean isEmpty()
{
    return front == rear;
}

@Override
public boolean isFull()
{
    return front == ((rear + 1) % N);
}

//return the number of indexes that are empty
public int getCapacityLeft()
{
    return N - 1 - count;
}   
}