public synchronized void putQuadTree(String key,QuadTree quadTree){
  quadTree.timestamp=System.currentTimeMillis();
  quadTreeMap.put(key,quadTree);
  cleanUpCache();
}

public synchronized void putQuadTree ( String key , QuadTree quadTree ) { quadTree . timestamp = System . currentTimeMillis ( ) ; quadTreeMap . put ( key , quadTree ) ; cleanUpCache ( ) ; }
place a quadtree in the cache update the timestamp
