What is the idiomatic way to exhaust a Queue in Java 8?

Question

Say I have a queue, and I want to exhaust it. The way I would do it is something like

void emptyQueue(Queue<T> q) {
  T i;
  while ((i = q.poll()) != null)
    consume(i);
}

but this feels like an archaic method.

I would like something more like the forEach method. It is, of course, present - the Queue being a Collection - but it iterates over the elements, rather than consuming them.

Ideally, I would have liked a pollEach method on Queue - but I can't seem to find anything appropriate.

How do you write this kind of code?

Answer 1

You can use your own generator that calls poll() on the queue:

Stream.generate( () -> q.poll() )
    .takeWhile(Objects::nonNull) //Note that this is only available in java 9
    .forEach(i -> consume(i));

This method is also an example of taking control of what passes the stream. You can manage things like blocking, etc. The takeWhile step in this case just shows how the end of the data can be detected.