Is there a fixed size Deque which removes old elements in Java?

Question

I need a queue like CircularFifoQueue in Apache Commons but with the ability to iterate elements backward. I.e. I need to insert elements in a fixed size queue with auto remove of old elements. But I need to iterate elements starting from the youngest element. Is there something available in Java?

Have you looked through the classes that implement the Java Deque interface (docs.oracle.com/javase/7/docs/api/java/util/Deque.html)? Any of the these classes may work for you as they provide a descendingIterator() method to, well, iterate in reverse order. — Michael Peacock
But any Deque has to have descendingIterator(). Still I didn't find Deque with auto-remove of old elements. — Oleksandr

Oleksandr Oleksandr · Accepted Answer · 2017-09-21T19:14:29

I can use something like this (need also rewrite other insert methods like push, pushLast...) but would like to hear other available solutions (if they exist).

public class ConcurrentFixedSizeLinkedDeque<T> extends ConcurrentLinkedDeque<T> {

    private int sizeLimit = Integer.MAX_VALUE;

    public ConcurrentFixedSizeLinkedDeque() {
    }

    public ConcurrentFixedSizeLinkedDeque(Collection<? extends T> c) {
        super(c);
    }

    public ConcurrentFixedSizeLinkedDeque(int sizeLimit) {
        if(sizeLimit<0) sizeLimit=0;
        this.sizeLimit = sizeLimit;
    }

    public ConcurrentFixedSizeLinkedDeque(Collection<? extends T> c, int sizeLimit) {
        super(c);
        if(sizeLimit<0) sizeLimit=0;
        this.sizeLimit = sizeLimit;
    }

    public int getSizeLimit() {
        return sizeLimit;
    }

    public void setSizeLimit(int sizeLimit) {
        this.sizeLimit = sizeLimit;
    }

    @Override
    public void addFirst(T e){
        while(size()>=this.sizeLimit){
            pollLast();
        }
        super.addFirst(e);
    }

    @Override
    public void addLast(T e){
        while(size()>=this.sizeLimit){
            pollFirst();
        }
        super.addLast(e);
    }
}

Is there a fixed size Deque which removes old elements in Java?

1 Answers