Is there a fixed sized queue which removes excessive elements?

Question

Actually the LinkedHashMap does exactly what you want. You need to override the removeEldestEntry method.

Example for a queue with max 10 elements:

  queue = new LinkedHashMap<Integer, String>()
  {
     @Override
     protected boolean removeEldestEntry(Map.Entry<Integer, String> eldest)
     {
        return this.size() > 10;   
     }
  };

If the "removeEldestEntry" returns true, the eldest entry is removed from the map.

Yes, Two

From my own duplicate question with this correct answer, I learned of two:

• EvictingQueue in Google Guava
• CircularFifoQueue in Apache Commons

---

I made productive use of the Guava EvictingQueue, worked well.

To instantiate an EvictingQueue call the static factory method create and specify your maximum size.

EvictingQueue< Person > people = com.google.common.collect.EvictingQueue.create( 100 ) ;  // Set maximum size to 100. 

I just implemented a fixed size queue this way:

public class LimitedSizeQueue<K> extends ArrayList<K> {

    private int maxSize;

    public LimitedSizeQueue(int size){
        this.maxSize = size;
    }

    public boolean add(K k){
        boolean r = super.add(k);
        if (size() > maxSize){
            removeRange(0, size() - maxSize);
        }
        return r;
    }

    public K getYoungest() {
        return get(size() - 1);
    }

    public K getOldest() {
        return get(0);
    }
}

There is no existing implementation in the Java Language and Runtime. All Queues extend AbstractQueue, and its doc clearly states that adding an element to a full queue always ends with an exception. It would be best ( and quite simple ) to wrap a Queue into a class of your own for having the functionality you need.

Once again, because all queues are children of AbstractQueue, simply use that as your internal data type and you should have a flexible implementation running in virtually no time :-)

UPDATE:

As outlined below, there are two open implementations available (this answer is quite old, folks!), see this answer for details.

This is what I did with Queue wrapped with LinkedList, It is fixed sized which I give in here is 2;

public static Queue<String> pageQueue;

pageQueue = new LinkedList<String>(){
            private static final long serialVersionUID = -6707803882461262867L;

            public boolean add(String object) {
                boolean result;
                if(this.size() < 2)
                    result = super.add(object);
                else
                {
                    super.removeFirst();
                    result = super.add(object);
                }
                return result;
            }
        };


....
TMarket.pageQueue.add("ScreenOne");
....
TMarket.pageQueue.add("ScreenTwo");
.....