It's a bounded queue (a first-in-first-out [queue][1] with a fixed capacity).

This particular queue always allows addition of elements and, when full, silently remove head element for newly added element.

In Java there is the [`CircularFifoQueue`][2] that works exactly this way (see also [Size-limited queue that holds last N elements in Java](http://stackoverflow.com/questions/5498865/size-limited-queue-that-holds-last-n-elements-in-java)).




  [1]: http://en.wikipedia.org/w/index.php?title=Queue_%28abstract_data_type%29
  [2]: http://commons.apache.org/proper/commons-collections/javadocs/api-release/org/apache/commons/collections4/queue/CircularFifoQueue.html