使用链表实现队列

队列接口：

public interface Queue<E> {
	int getSize();
	boolean isEmpty();
	void enqueue(E e);
	E dequeue();
	E getFront();
}

实现类：

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);
		}

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

	private Node head, tail;
	private int size;

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

	public int getSize() {
		return size;
	}

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

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

	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;
	}

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

	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(queue);
			if (i % 3 == 2) {
				queue.dequeue();
				System.out.println(queue);
			}
		}
	}
}