code: public void tick() {
          ticks.incrementAndGet();
  
          if (logger.isDebugEnabled()) {
              logger.debug("Tick!");
          }
  
          List<CacheItem> itemsToRefresh = new ArrayList<CacheItem>();
  
          try {
              Collection<String> scopes = cacheStoreAdapter.getScopes();
              if (CollectionUtils.isNotEmpty(scopes)) {
                  for (String scope : scopes) {
                      Collection<Object> keys = cacheStoreAdapter.getKeys(scope);
                      if (CollectionUtils.isNotEmpty(keys)) {
                          for (Object key : keys) {
                              CacheItem item = cacheStoreAdapter.get(scope, key);
                              if (item != null) {
                                  doChecks(item, itemsToRefresh);
                              } else {
                                  if (logger.isDebugEnabled()) {
                                      logger.debug(item + " was removed before it could be checked for " +
                                                   "expiration/refresh");
                                  }
                              }
                          }
                      }
                  }
              }
  
              if (cacheRefresher != null && CollectionUtils.isNotEmpty(itemsToRefresh)) {
                  cacheRefresher.refreshItems(itemsToRefresh, this);
              }
          } catch (Exception ex) {
              logger.warn("Exception while checking items for expiration/refresh", ex);
          }
      }
docs: Called when a tick occurs. A tick is a logical unit of time. It basically symbolizes the time span between
  calls to this method (i.e. 15 mins) by a job scheduler like Quartz.
  <p/>
  Checks if some of the {@link CacheItem}s in the cache have expired or need to be refreshed. If the item
  has expired, it is removed from the cache. If it needs to be refreshed, it is added to a list of items that
  need to be refreshed that is later passed to the {@link CacheRefresher}.