linked list queue

// This queue implementation uses a linked list and can dynamically grow and shrink as needed.

public class LinkedListQueue {

    // Node class for linked list
    private class Node {

        int data;
        Node next;

        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }

    private Node front; // Points to the front node
    private Node rear;  // Points to the rear node
    private int size;   // Number of elements in the queue

    // Constructor to initialize an empty queue
    public LinkedListQueue() {
        front = null;
        rear = null;
        size = 0;
    }

    // Add an item to the rear of the queue
    public void enqueue(int item) {
        Node newNode = new Node(item);
        if (isEmpty()) {
            front = newNode;
        } else {
            rear.next = newNode;
        }
        rear = newNode;
        size++;
    }

    // Remove and return the front item of the queue
    public int dequeue() {
        if (isEmpty()) {
            System.out.println("Queue is empty. Cannot dequeue.");
            return Integer.MIN_VALUE;
        }
        int item = front.data;
        front = front.next;
        if (front == null) {
            rear = null; // Reset rear when queue becomes empty
        }
        size--;
        return item;
    }

    // Return the front item without removing it
    public int peek() {
        if (isEmpty()) {
            System.out.println("Queue is empty. No peek value.");
            return Integer.MIN_VALUE;
        }
        return front.data;
    }

    // Return true if the queue is empty
    public boolean isEmpty() {
        return front == null;
    }

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

    // Print the current state of the queue
    public void printState(String stepTitle, String enqueueItems, Integer dequeued) {
        System.out.println("------------" + stepTitle + "---------------");
        if (enqueueItems != null) {
            System.out.println("Enqueue: " + enqueueItems + ";");
        }
        if (dequeued != null) {
            System.out.println("Dequeued: " + dequeued + ";");
        }
        System.out.println("Current size: " + size);
        System.out.println("Peek value: " + (isEmpty() ? "N/A" : peek()));

        // Mimic array-like content display
        System.out.print("Linked list content: ");
        Node current = front;
        while (current != null) {
            System.out.print(current.data + " ");
            current = current.next;
        }

        // Show visible queue (same as content in linked list)
        System.out.print("\nVisible queue: ");
        current = front;
        while (current != null) {
            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println("\n");
    }

    // Demonstration of linked list queue operations
    public static void main(String[] args) {
        LinkedListQueue queue = new LinkedListQueue();

        // Step 1: Enqueue multiple elements
        queue.enqueue(10);
        queue.enqueue(20);
        queue.enqueue(30);
        queue.printState("Step 1 : enqueue", "10, 20, 30", null);

        // Step 2: Dequeue one element
        int removed = queue.dequeue();
        queue.printState("Step 2 : dequeue", null, removed);

        // Step 3: Enqueue additional elements
        queue.enqueue(40);
        queue.enqueue(50);
        queue.enqueue(60);
        queue.printState("Step 3 : enqueue", "40, 50, 60", null);
    }
}