Java通过链表实现队列

class LinkedQueue<T> {
    /**
     * 队列大小，由构造函数初始化
     */
    private int maxSize;

    /**
     * 队头
     */
    private Node front = null;

    /**
     * 队尾
     */
    private Node rear = null;

    /**
     * 队列实际元素个数
     */
    private int nItems;

    /**
     * 初始化队列，并指定队列长度
     *
     * @param maxSize
     */
    public LinkedQueue(int maxSize) {
        this.maxSize = maxSize;
        front = null;
        rear = null;
        this.nItems = 0;
    }

    /**
     * 讲一个数据放入队列
     *
     * @param data
     */
    public void enqueue(T data) {
        Node node = new Node(data);
        if (isEmpty()) {
            front = node;
            front.next = null;
            rear = node;
            rear.pre = null;
            nItems++;
            return;
        }
        if (size() == 1) {
            rear = node;
            front.next = rear;
            rear.pre = front;
            nItems++;
            return;
        }
        if (isFull()) {
            System.out.print("超过队列已满，无法入队");
            return;
        }
        node.pre = rear;
        rear.next = node;
        rear = node;
        nItems++;
    }

    /**
     * 将数据出队
     *
     * @return
     */
    public T dequeue() {
        Node temp = null;
        if (isEmpty()) {
            System.out.println("队列已空，无法出队");
            return null;
        }
        if (size() == 1) {
            temp = front;
            front = null;
            rear = null;
            nItems--;
            return temp.data;
        }
        if (size() == 2) {
            temp = front;
            front = rear;
            front.next = null;
            rear.pre = null;
            nItems--;
            return temp.data;
        }
        temp = front;
        front = front.next;
        nItems--;
        return temp.data;
    }

    /**
     * 判断队列是否为空
     *
     * @return
     */
    public boolean isEmpty() {
        return nItems == 0;
    }

    /**
     * 判断队列是否已满
     *
     * @return
     */
    public boolean isFull() {
        return nItems == maxSize;
    }

    /**
     * 获取队列的实际数据个数
     *
     * @return
     */
    public int size() {
        return nItems;
    }

    /**
     * 将数据封装成节点
     *
     * @author John
     *
     */
    private class Node {
        T data;
        Node next;
        Node pre;

        public Node(T data) {
            this.data = data;
        }
    }
}