固定大小的Java队列数据结构

Question

I have a stream of network data coming in every few ms. I need remove the first element, and add an element to the end of a fixed-sized list when this happens (ie "shift"). The elements are simple float s.

What data structure should I use, and is there an example usage? Thanks.

Answer 1

You've got several options. The easiest would of course to just use a Queue , Java's got some implementations for you ( arrayblocking , concurrentlinked ). You could overwrite any of them to add a shift method:

public E shift(E newElement) {
    E old = take();
    put(newElement);
    return old;
}

To make this threadsafe, you'll need some synchronization.

If, for some reason, you prefer other collections, that's possible, too. Mind that these might not be thread safe. I would not use an ArrayList, because of rather bad complexities, but a LinkedList should be fine. Overwriting it would need this shift:

public E shift(E newElement) {
    E old = getFirst();
    addLast(newElement);
    return old;
}

As long as you use only the shift method, you can be sure of the fixed size. If you want to force it, you'll have to overwrite more methods, of use a delegator.

Answer 2

I don't exactly know how you want to access the data from this ever-changing queue, but I suggest a LinkedBlockingQueue<Float> or ArrayBlockingQueue<Float> along with a thread to wait for & process input. You can add elements to the queue from any thread (eg your network thread), and process elements when they become available. This way you are guaranteed to not loose any data unlike your current approach may (because data would be lost if more elements are written than processed unless you prevent writes while the data is being processed).