size not counting properly in linked list implementation of queue in java

Question

I'm trying to make a linked list implementation of a queue in Java and in my driver program after I dequeue some elements, the size is not adjusting to be a lower number like it should. Here's the code and the output is below it.

This is the linked list queue implementation:

import java.util.LinkedList;

//implementation of a queue by using a linked list
public class Queue<T> {
    //declaring array list to store and manipulate data 
    //using predefined methods

    private LinkedList<T> list;
    int count, front, rear;

    public Queue() {
        list= new LinkedList<T>();
        count=front=rear=0;
    }

    //Adds given element to rear of queue
    public void enqueue (T element) {
        if(front==rear) {
            list.add(front, element);
            rear++;
        }
        else {
            list.add(rear, element);
            rear++;
        }
        count++;
    }

    //removes element at queue front
    public T dequeue() {
        if(list.isEmpty()) {
            System.out.println("Queue is empty");
            return null;
        }

        T result = list.get(front);
        front++;
        count--;
        return result;
    }

    //returns reference to element at queue front
    public T first() {
        return list.get(front);
    }

    //returns true if queue is empty
    public boolean isEmpty() {
        if(list.isEmpty())
            return true;
        else
            return false;
    }

    //returns number of elements in the queue
    public int size() {
        return list.size();
    }

    //returns string representation of queue
    public String toString() {
        String result = "";
        for(int i=front;i<rear;i++) 
            result+=list.get(i)+" ";
        return result;
    }

}

This is the driver class.

/*Demonstrates the use of a queue implemented by
 * using a linked list*/
public class QueueLinkedListDemo {

    public static void main(String[] args) {
        Queue<Character> charList = new Queue<Character>();

//display size of queue
        System.out.println("The size of the queue is " + charList.size());

        //adding elements to queue
        System.out.println("Calling enqueue() to add 'a' to the queue");
        charList.enqueue('a');
        System.out.println("Calling enqueue() to add 'b' to the queue");
        charList.enqueue('b');

        //display size of queue
        System.out.println("The size of the queue is " + charList.size());

        System.out.println("Calling dequeue() method to remove an element from the queue " + charList.dequeue());
        System.out.println("Calling toString() method to display queue elements " + charList.toString());
        //display first element of queue
        System.out.println("The first element in queue is " + charList.first());
        //display size of queue
        System.out.println("The size of the queue is " + charList.size());

    }

}

Output of this code: The size of the queue is 0 Calling enqueue() to add 'a' to the queue Calling enqueue() to add 'b' to the queue The size of the queue is 2 Calling dequeue() method to remove an element from the queue a Calling toString() method to display queue elements b The first element in queue is b The size of the queue is 2

Notice the size did not change from 2 to 1 when an element was removed from the queue. How can this be fixed?

Answer 1

your list never decreases in size. To correct this, you would need to do:

    public T dequeue() {
        if(list.isEmpty()) {
            System.out.println("Queue is empty");
            return null;
        }

        T result = list.remove(0);
        return result;
   }

and this would render count, rear, front useless.