public void enqueue(E e){
	if(tail == null){
		tail = new Node(e);
		head = tail;
	}
	else{
		tail.next = new Node(e);
		tail = tail.next;
	}
	size++;
}

实现添加队列的方法我有一些疑问：在多次调用该方法的过程中，只有第一次进行了tail是否为空的判断是成功的，因此运行了一次head = tail。但是之后的方法调用过程中没有调用head的痕迹，为什么head中Node对象依然可以不断变化。

以下是完整的代码：

public class LinkedListQueue<E> implements Queue<E>{

    private class Node{
        public E e;
        public Node next;

        public Node(E e, Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e){
            this(e, null);
        }

        public Node(){
            this(null, null);
        }

        @Override
        public String toString(){
            return e.toString();
        }
    }

    private Node head, tail;
    private int size;

    public LinkedListQueue(){
        head = null;
        tail = null;
        size = 0;
    }

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

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

    @Override
    public void enqueue(E e) {
        if(tail == null){
            tail = new Node(e);
            head = tail;
        }
        else{
            tail.next = new Node(e);
            tail = tail.next;
        }
        size++;
    }

    @Override
    public E dequeue() {
        if(isEmpty())
            throw new IllegalArgumentException("Cannot dequeue from an empty queue");

        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if(head == null)
            tail = null;
        size--;
        return retNode.e;
    }

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

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append("Queue: front ");

        Node cur = head;
        while(cur != null){
            res.append(cur + "->");
            cur = cur.next;
        }
        res.append("NULL tail");
        return res.toString();
    }

    public static void main(String[] args) {

        LinkedListQueue<Integer> queue = new LinkedListQueue<>();
        for(int i = 0; i < 10; i++){
            queue.enqueue(i);
            System.out.println("---------------------------第" + (i+1) + "次循环---------------------------------" );
            System.out.println("head对象的哈希值为：" + queue.head.hashCode());
            System.out.println("tail对象的哈希值为：" + queue.tail.hashCode());
            System.out.println("--------------------------------------------------------------------");
            System.out.println(queue);

        }
    }
}

运行结果：
---------------------------第1次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：586617651
--------------------------------------------------------------------
Queue: front 0->NULL tail
---------------------------第2次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：998351292
--------------------------------------------------------------------
Queue: front 0->1->NULL tail
---------------------------第3次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：1684106402
--------------------------------------------------------------------
Queue: front 0->1->2->NULL tail
---------------------------第4次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：335471116
--------------------------------------------------------------------
Queue: front 0->1->2->3->NULL tail
---------------------------第5次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：1308927845
--------------------------------------------------------------------
Queue: front 0->1->2->3->4->NULL tail
---------------------------第6次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：2017354584
--------------------------------------------------------------------
Queue: front 0->1->2->3->4->5->NULL tail
---------------------------第7次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：391447681
--------------------------------------------------------------------
Queue: front 0->1->2->3->4->5->6->NULL tail
---------------------------第8次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：1935637221
--------------------------------------------------------------------
Queue: front 0->1->2->3->4->5->6->7->NULL tail
---------------------------第9次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：403424356
--------------------------------------------------------------------
Queue: front 0->1->2->3->4->5->6->7->8->NULL tail
---------------------------第10次循环---------------------------------
head对象的哈希值为：586617651
tail对象的哈希值为：321142942
--------------------------------------------------------------------
Queue: front 0->1->2->3->4->5->6->7->8->9->NULL tail