Question

Write a method for the Queue class in the queue.java program (Listing 4.4) that displays the contents of the queue. Note that this does not mean simply displaying the contents of the underlying array. You should show the queue contents from the first item inserted to the last, without indicating to the viewer whether the sequence is broken by wrapping around the end of the array. Be careful that one item and no items display properly, no matter where front and rear are.

// Queue.java
// demonstrates queue
// to run this program: C>java QueueApp
////////////////////////////////////////////////////////////////

class Queue
{
private int maxSize;
private long[] queArray;
private int front;
private int rear;
private int nItems;

public Queue(int s) // constructor
{
maxSize = s;
queArray = new long[maxSize];
front = 0;
rear = -1;
nItems = 0;
}

public void insert(long j) // put item at rear of queue
{
if(rear == maxSize-1) // deal with wraparound
rear = -1;
queArray[++rear] = j; // increment rear and insert
nItems++; // one more item
}

public long remove() // take item from front of queue
{
long temp = queArray[front++]; // get value and incr front
if(front == maxSize) // deal with wraparound
front = 0;
nItems--; // one less item
return temp;
}

public long peekFront() // peek at front of queue
{
return queArray[front];

}

public boolean isEmpty() // true if queue is empty
{
return (nItems==0);
}

public boolean isFull() // true if queue is full
{
return (nItems==maxSize);
}

public int size() // number of items in queue
{
return nItems;
}

}

class QueueApp
{
public static void main(String[] args)
{
Queue theQueue = new Queue(5);

theQueue.insert(10); // insert 4 items
theQueue.insert(20);
theQueue.insert(30);
theQueue.insert(40);

theQueue.remove(); // remove 3 items
theQueue.remove(); // (10, 20, 30)
theQueue.remove();

theQueue.insert(50); // insert 4 more items
theQueue.insert(60); // (wraps around)
theQueue.insert(70);
theQueue.insert(80);

while( !theQueue.isEmpty() ) // remove and display
{ // all items
long n = theQueue.remove(); // (40, 50, 60, 70, 80)
System.out.print(n);
System.out.print(" ");
}
System.out.println("");
} // end main()
} // end class QueueApp

Answer 1

//For any queries, feel free to comment.

**CODE**

class Queue
    {
    private int maxSize;
    private long[] queArray;
    private int front;
    private int rear;
    private int nItems;

    public Queue(int s) // constructor
    {
        maxSize = s;
        queArray = new long[maxSize];
        front = 0;
        rear = -1;
        nItems = 0;
    }

    public void insert(long j) // put item at rear of queue
    {
        if(rear == maxSize-1) // deal with wraparound
            rear = -1;
        queArray[++rear] = j; // increment rear and insert
        nItems++; // one more item
    }

    public long remove() // take item from front of queue
    {
        long temp = queArray[front++]; // get value and incr front
        if(front == maxSize) // deal with wraparound
            front = 0;
        nItems--; // one less item
        return temp;
    }

    public void printQueue(){
        int count = nItems;

        int x = front;

        while(count > 0){
            System.out.print(queArray[x] + " ");
            x = (x+1)%maxSize;
            count--;
        }

        System.out.println();
    }

    public long peekFront() // peek at front of queue
    {
        return queArray[front];

    }

    public boolean isEmpty() // true if queue is empty
    {
        return (nItems==0);
    }

    public boolean isFull() // true if queue is full
    {
        return (nItems==maxSize);
    }

    public int size() // number of items in queue
    {
        return nItems;
    }

}

public class Main
{
    public static void main(String[] args)
    {
        Queue theQueue = new Queue(5);

        theQueue.insert(10); // insert 4 items
        theQueue.insert(20);
        theQueue.insert(30);
        theQueue.insert(40);

        theQueue.remove(); // remove 3 items
        theQueue.remove(); // (10, 20, 30)
        theQueue.remove();

        theQueue.insert(50); // insert 4 more items
        theQueue.insert(60); // (wraps around)
        theQueue.insert(70);
        theQueue.insert(80);
      
        System.out.print("Queue is: ");
        theQueue.printQueue();
      
    } // end main()
} // end class QueueApp

**SNIPPET**