队列的一种实现：循环队列

class CircularQueue<T> {
    
    private Object[] data; //数据存储数组
    private int head; //队列头指针
    private int tail; //队列尾指针
    private int size; //队列长度

    /**
     * 初始化
     *
     * @param k
     */
    public CircularQueue(int k) {
        data = new Object[k]; //数组初始化
        head = -1;
        tail = -1;
        size = k;
    }

    /**
     * 元素入队，成功则返回true，否则false
     *
     * @param value
     * @return
     */
    public boolean put(T value) {
        if (isFull() == true) { //入队，判断队满
            return false;
        }
        if (isEmpty() == true) { //入队，队空，则head置0
            head = 0;
        }
        tail = (tail + 1) % size; //循环队列，队尾循环移动，所以使用取余的方式移动队尾
        data[tail] = value; //将入队元素放入队列
        return true;
    }

    /**
     * 出队
     *
     * @return
     */
    public T remove() {
        T result = null;
        if (isEmpty() == true) { //出队、判断队空
            return result;
        }
        if (head == tail) { //队首 队尾重合，则当前队列只剩唯一元素
            result = (T) data[tail];
            head = -1;
            tail = -1;
            return result;
        }
        result = (T) data[head];
        data[head] = null;
        head = (head + 1) % size;
        return result;
    }

    /**
     * 获取队首元素
     *
     * @return
     */
    public T head() {
        if (isEmpty() == true) {
            return null;
        }
        return (T) data[head];
    }

    /**
     * 获取队尾元素
     *
     * @return
     */
    public T tail() {
        if (isEmpty() == true) {
            return null;
        }
        return (T) data[tail];
    }

    /** 对空判断
     *
     * @return
     */
    public boolean isEmpty() {
        return head == -1;
    }

    /** 对满判断
     *
     * @return
     */
    public boolean isFull() {
        return ((tail + 1) % size) == head; //尾指针再移动一位则与头指针重合
    }

    public String toString(){
        StringBuilder str = new StringBuilder();
        for (Object datum : data) {
            if (datum != null) {
                str.append(datum);
            }
        }
        return str.toString();
    }

    public static void main(String[] args) {
        CircularQueue queue = new CircularQueue<Integer>(5);
        queue.put(5);
        queue.put(3);
        queue.put(1);
        System.out.println(queue);
        System.out.println(queue.head());
        System.out.println(queue.tail());
        queue.remove();
        System.out.println(queue);
        System.out.println(queue.head());
        System.out.println(queue.tail());
    }
}