链表LinkedList实现队列

Queue.java（队列接口）

public interface Queue<E> {
    void enqueue(E e);//入队
    E dequeue();//出队
    E getFront();//获取队首元素
    int getSize();//获取队列中元素个数
    boolean isEmpty();//判断队列是否为空
}

LinkedListQueue.java（链表队列）
带尾节点的链表实现队列，没有设置虚拟头节点

//链表头是队列头，出队O(1);链表尾是队列尾,入队O(1)    
public class LinkedListQueue<E> implements Queue<E> {
    private class Node {
    // 内部类将节点设为私有 隐藏实现细节
        public E e;// 元素
        public Node next;// next指针
        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;// 定义头节点，尾节点
    private int size;
    public LinkedListQueue() {
        // TODO Auto-generated constructor stub
        head = null;
        tail = null;
        size = 0;
    }
    @Override
    public void enqueue(E e) {
        // TODO Auto-generated method stub
        if (tail == null) {
     // tail == null是尾节点为空，也就是队列为空的时候，否则tail应该指向尾节点
            tail = new Node(e);// 传入要插入的节点
            head = tail;
        } else {
            tail.next = new Node(e);// 如果tail不为空，在tail.next处插入节点
            tail = tail.next;// tail后移
        }
        size++;
    }
    @Override
    public E dequeue() {
        // TODO Auto-generated method stub
        if (isEmpty())
            try {
                throw new Exception("队列为空");
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        Node retNode = head;// 出队的节点就是head所指向的节点
        head = head.next;// head后移
        retNode.next = null;
        if (head == null)// 如果队列中只有一个元素
            tail = null;
        size--;
        return retNode.e;
    }
    @Override
    public E getFront() {
        // TODO Auto-generated method stub
        if (isEmpty())
            try {
                throw new Exception("队列为空");
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        return head.e;
    }
    @Override
    public int getSize() {
        // TODO Auto-generated method stub
        return size;
    }
    @Override
    public boolean isEmpty() {
        // TODO Auto-generated method stub
        return size == 0;
    }
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("Queue：front ");
        for (Node cur = head; cur != null; cur = cur.next)
            res.append(cur + "->");
        res.append("NULL tail");
        return res.toString();
    }
}

测试（main）

public class LinkedListQueueTest {
    public static void main(String[] args) {
        LinkedListQueue<Integer> loopqueue = new LinkedListQueue<>();
        for (int i = 0; i < 5; i++) {
            loopqueue.enqueue(i);
            System.out.println(loopqueue);
        }
        loopqueue.dequeue();
        System.out.println(loopqueue);
    }
}