Linked Queue

LinkedQueue.java

package com.hrishikesh.narashima.ch5queue;


import com.hrishikesh.narashima.ch4stack.ListNode;

import java.util.Objects;
import java.util.StringJoiner;

/**
 *
 * Linked Queue
 * Created by hrishikesh.mishra
 */
public class LinkedQueue<E> implements Queue<E> {

    private ListNode<E> front;
    private ListNode<E> rear;
    private int size;

    @Override
    public void enQueue(E element) {
        ListNode<E> node = new ListNode<E>(element);
        if(Objects.isNull(rear))
            rear = node;
        else
            rear.setNext(node);
        size++;
    }

    @Override
    public E deQueue() {
        if(isEmpty())
            throw new IllegalStateException("Queue is empty");

        ListNode<E> node = front;
        front = front.getNext();
        node.setNext(null);
        size--;
        return node.getData();
    }

    @Override
    public E front() {
        if(isEmpty())
            throw new IllegalArgumentException("Queue is empty");
        return front.getData();
    }

    @Override
    public int size() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return (size == 0);
    }

    @Override
    public String toString() {
        StringJoiner joiner = new StringJoiner(", ", "[", "]");
        ListNode<E> node = new ListNode<>();
        while (!Objects.isNull(node)){
            joiner.add(String.valueOf(node.getData()));
            node = node.getNext();
        }
        return joiner.toString();
    }
}

class LinkedQueueTest{
    public static void main(String[] args) {
        Queue<Integer> queue = new FixedSizeArrayQueue<Integer>(4);
        queue.enQueue(1);
        queue.enQueue(2);
        queue.enQueue(3);
        System.out.println("Queue after enqueue (1, 2, 3) : " + queue);
        System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
        System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
        queue.enQueue(4);
        queue.enQueue(5);
        System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
        queue.enQueue(6);
        System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
        System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
        System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
    }
}