Question

QUEUEBOX: Using an Array of initial size of five (5) for storage, start with the following generic class declaration for QueueBox: public class QueueBox<E> { private E[] elements = (ED))( new Object[5]); private int front_idx = 0; private int rear_idx = 0; private int count = 0; Hint: use the count variable to keep track of how many elements are in the queue (increment count when enqueing and decrement when dequeing). Makes it a lot easier to determine if the array is full and for the other functions as well. Of course you may add or modify variables to this class BUT you MUST use a GENERIC array of initial size 5 and your queue MUST be a circular queue. Ensure your QueueBox can do the following: boolean addE e) Adds e to the queue (enqueue). returns true. Throws NullPointerException if e is null. E remove Removes element in the front of the queue (dequeue) and returns it. NoSuchElementException is thrown if this queue is empty

Answer 1

Hi. I have answered this same question before. Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

// QueueBox.java

import java.util.NoSuchElementException;

public class QueueBox<E> {

    private E[] elements = (E[]) (new Object[5]);

    private int front_idx = 0;

    private int rear_idx = 0;

    private int count = 0;

    // method to add an element to the rear end of the queue

    public boolean add(E value) {

        // resizing array if full

        if (count == elements.length) {

             resize(elements.length * 2);

        }

        // adding value to index rear_idx

        elements[rear_idx] = value;

        // updating rear_idx, wrapping around from the beginning if necessary

        rear_idx = (rear_idx + 1) % elements.length;

        // updating count

        count++;

        return true;

    }

    // private method to resize the array when full

    private void resize(int newCap) {

        // creating a new array

        E[] newArr = (E[]) new Object[newCap];

        int i = front_idx;

        int index = 0;

        // copying elements from old array to new

        while (index < count) {

             newArr[index] = elements[i];

             // moving to next index, wrapping around from 0 if go out of range

             i = (i + 1) % elements.length;

             index++;

        }

        // replacing old array with new, updating front and back indices

        elements = newArr;

        front_idx = 0;

        rear_idx = index;

        // displaying a message letting user know that array has been resized

        System.out.println("Array resized to " + newCap);

    }

   

    //removes and returns the top element

    public E remove() {

        if (isEmpty()) {

             // empty

             throw new NoSuchElementException();

        }

        // taking element at front

        E elem = elements[front_idx];

        // updating front index, wrapping around from the beginning if necessary

        front_idx = (front_idx + 1) % elements.length;

        //updating count and returning item

        count--;

        return elem; // returning removed element

    }

   

    //returns the element without removing

    public E element() {

        if (isEmpty()) {

             // empty

             throw new NoSuchElementException();

        }

        // element at front index

        return elements[front_idx];

    }

   

    // returns true if queue is empty

    public boolean isEmpty() {

        return count == 0;

    }

   

    //returns the current number of elements in queue

    public int size() {

        return count;

    }

}

// QueueBoxDriver.java

public class QueueBoxDriver {

    public static void main(String[] args) {

        // creating a QueueBox of integers

        QueueBox<Integer> que = new QueueBox<Integer>();

        // adding numbers between 0 and 59999

        for (int i = 0; i < 60000; i++) {

             que.add(i);

        }

        // removing first 50000 numbers

        for (int i = 0; i < 50000; i++) {

             que.remove();

        }

        // printing the rest. it should be values between 50000 and 59999

        while (!que.isEmpty()) {

            System.out.println(que.remove());

        }

    }

}

/*OUTPUT (partial)*/

Array resized to 20

Array resized to 40

Array resized to 80

Array resized to 160

Array resized to 320

Array resized to 640

Array resized to 1280

Array resized to 2560

Array resized to 5120

Array resized to 10240

Array resized to 20480

Array resized to 40960

Array resized to 81920

50000

50001

50002

50003

50004

50005

50006

50007

50008

50009

50010

50011

50012

50013

50014

50015

50016

50017

50018

50019

50020

50021

50022

50023

50024

50025

50026

50027

50028

50029

50030

…

…

…

59964

59965

59966

59967

59968

59969

59970

59971

59972

59973

59974

59975

59976

59977

59978

59979

59980

59981

59982

59983

59984

59985

59986

59987

59988

59989

59990

59991

59992

59993

59994

59995

59996

59997

59998

59999