Queue Implementation Using Linked List in Java

// Java Program to Implement Queue
// Using Linked List

// Node Class
class Node {
    int data;
    Node next;

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

// Queue Class
class Queue {
    Node front, rear;
      int length;

      // Constructor
    public Queue() {
        this.front = this.rear = null;
          this.length=0;
    }

      // Adding Element in the LinkedList/Queue
    void enqueue(int key) {
          this.length++;
        Node temp = new Node(key);
        
          if (this.rear == null) {
            this.front = this.rear = temp;
            return;
        }
          
        this.rear.next = temp;
        this.rear = temp;
    }

      // Removing Element from the top
    void deque() {
        if (this.front == null)
            return;
          
        Node temp = this.front;
        this.front = this.front.next;
          
          // If Queue is Empty
        if (this.front == null)
            this.rear = null;
      
          // Removing the Front Element
        temp.next = null;  
    }

      // Checking on Front Element
    int peek() {
        if (this.front != null)
            return this.front.data;
      
          // Return Exception
        return Integer.MIN_VALUE;  
    }
  
      // Return the Size of Queue
      int size(){
          return this.length;
    }
  
      // Printing the Elements of Queue
      void printQueue(){
          Node temp=this.front;
          
          System.out.print("Element of Queue : ");
      
          while(temp!=null){
            System.out.print(temp.data+" ");
              temp=temp.next;
        }
          System.out.println();
    }
}

// Driver Class
public class Main {
      // Main Function
    public static void main(String[] args) {
        Queue q = new Queue();
        q.enqueue(10);
        q.enqueue(20);
          
          q.printQueue();
          System.out.println("Size :" + q.size());
        q.deque();
        q.deque();
        q.enqueue(30);
        q.enqueue(40);
        q.enqueue(50);
          q.printQueue();
          System.out.println("Size :" + q.size());
        System.out.println("Front item is: " + q.peek());
    }
}