Is there a cyclic List,Queue, whatever else in standard Java libraries?

Question

I am looking for cyclic collection in Java. I have some players in Array (they wait for their turn) but I would like to change Array to cyclic collection so it will be easier to get next player.(I know how it can be done otherwise, but I'd like to use cyclic collection already prepared in Java).

Have you considered a queue? But otherwise, no, a cyclic collection isn't in the standard Java libraries as far as I know. — awksp, May 14 '14 at 22:18
But you can make it behave like it's cyclic. Pop something off, do something with it, push it back on after. — awksp, May 14 '14 at 22:20
See also http://stackoverflow.com/questions/7266042/java-ring-buffer — Raedwald, May 14 '14 at 22:41
What @Ypnypn said. There is rarely a need to get any more complicated than that. — Hot Licks, May 14 '14 at 23:07

OldCurmudgeon · Answer 1 · 2014-05-14T23:26:31.577

You can make any Iterable into a cyclic collection. Just keep requesting Iterators forever.

class Ring<T> implements Iterable<T> {
    // Source of all Iterators.
    final Iterable<T> it;
    // Current Iterator we are consuming.
    Iterator<T> i;

    public Ring(Iterable<T> it) {
        this.it = it;
        i = it.iterator();
    }

    @Override
    public Iterator<T> iterator() {
        return new Iterator<T> () {

            @Override
            public boolean hasNext() {
                // There's always a next for a Ring.
                return true;
            }

            @Override
            public T next() {
               if ( !i.hasNext() ) {
                   // Iterator is exhausted - make a new one!
                   i = it.iterator();
               }
               return i.next();
            }

        };
    }
}

public void test() {
    Ring<String> r = new Ring<>(Arrays.asList("One", "Two", "Three"));
    int printed = 0;
    for (String s : r) {
        System.out.println(s);
        if (++printed > 10) {
            break;
        }
    }
}

Note that there is a strange edge case when the wrapped Iterable delivers empty iterators but I leave that detail to the student.

Is it only I that read "make a new one!" like a little kid saying "let's have more cake!"? — Andrew Gies, May 14 '14 at 23:14

Is there a cyclic List,Queue, whatever else in standard Java libraries?

1 Answers1