numResidentTiles++;  if (numResidentTiles > MAX_RESIDENT_TILES)
cacheCursor++; if (cacheCursor == MAX_RESIDENT_TILES)
   void validateTile(int tilex, int tiley)   {      int whichTile = (tiley * tileWidth) + tilex;      if (tiles[whichTile].isValid())      {         return;      }      // The tile isn't in memory, so we need to validate it, then make sure we       // haven't loaded too many tiles      tiles[whichTile].validate();      numResidentTiles++;      if (numResidentTiles > MAX_RESIDENT_TILES)      {         // we've loaded too many tiles, we need to expire one         expireLRUTile();      }   }