642. moving average from data stream

public class  {
    private int size;
    private Queue<Integer> queue;
    private double sum; 

    /*
    * @param size: An integer
    */public (int size) {
        // do intialization if necessary
        this.queue = new LinkedList<Integer>();
        this.size = size;
        this.sum = 0;
    }

    /*
     * @param val: An integer
     * @return:  
     */
    public double next(int val) {
        // write your code here
        sum += val;
        queue.offer(val);
        if (queue.size() > size) {
            sum = sum - queue.poll();

        }
        return sum / queue.size();
        // 怎么把元素取出来，按原先的顺序放进去?
        //不需要这样，只要维持一个sum就好

    }
}