用Java编写遍历链表的dequeue()函数

public class DequeueExample {
    private Node head;
    private Node tail;
    
    private class Node {
        int data;
        Node next;
        
        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }
    
    public void enqueueFront(int data) {
        Node newNode = new Node(data);
        
        if (head == null) {
            head = newNode;
            tail = newNode;
        } else {
            newNode.next = head;
            head = newNode;
        }
    }
    
    public void enqueueRear(int data) {
        Node newNode = new Node(data);
        
        if (head == null) {
            head = newNode;
            tail = newNode;
        } else {
            tail.next = newNode;
            tail = newNode;
        }
    }
    
    public int dequeueFront() {
        if (head == null) {
            throw new NoSuchElementException("Queue is empty");
        }
        
        int data = head.data;
        head = head.next;
        
        if (head == null) {
            tail = null;
        }
        
        return data;
    }
    
    public int dequeueRear() {
        if (head == null) {
            throw new NoSuchElementException("Queue is empty");
        }
        
        int data = tail.data;
        
        if (head == tail) {
            head = null;
            tail = null;
        } else {
            Node currentNode = head;
            while (currentNode.next != tail) {
                currentNode = currentNode.next;
            }
            currentNode.next = null;
            tail = currentNode;
        }
        
        return data;
    }
    
    public void printQueue() {
        Node currentNode = head;
        while (currentNode != null) {
            System.out.print(currentNode.data + " ");
            currentNode = currentNode.next;
        }
        System.out.println();
    }
    
    public static void main(String[] args) {
        DequeueExample dequeue = new DequeueExample();
        
        dequeue.enqueueFront(1);
        dequeue.enqueueFront(2);
        dequeue.enqueueRear(3);
        dequeue.enqueueRear(4);
        
        dequeue.printQueue();  // 输出：2 1 3 4
        
        System.out.println(dequeue.dequeueFront());  // 输出：2
        System.out.println(dequeue.dequeueRear());   // 输出：4
        
        dequeue.printQueue();  // 输出：1 3
    }
}