MergingQueue

MergingQueue.java

/**
 * A merging FIFO queue. The entries are merged on a key and so the queue interface
 * is not appropriate. Note that the FIFO applies to the keys, not the values.
 * 
 * @author nitsanw
 *
 * @param <KEY>
 * @param <VAL>
 */
public interface MergingQueue<KEY, VAL> {
  /**
   * Removed the tail entry of the queue and returns it.
   * 
   * @return the latest value for the oldest key in the queue, or null if queue is empty.
   */
  VAL poll();

  /**
   * Inserts a new entry to the queue. If a value for this key already exists then the
   * original order is preserved while the value is replaced.
   * 
   * @param key not null
   * @param val not null 
   */
  void offer(KEY key, VAL val);

  /**
   * @return true if queue is empty, false otherwise
   */
  boolean isEmpty();

  /**
   * Clears the queue of all entries
   */
  void clear();
}