code: @Override
      public void purge() {
          try {
              this.lock.writeLock().lock();
              this.lruCache.clear();
          } finally {
              this.lock.writeLock().unlock();
          }
  
          deleteDirectory(this.cacheDirectory);
      }
docs: Purges this cache.
  <p/>
  Calls to {@link #get(Job)} issued after purging will not return any tiles added before the purge operation.
  Purging will also delete the cache directory on disk, freeing up disk space.
  <p/>
  Applications should purge the tile cache when map model parameters change, such as the render style for locally
  rendered tiles, or the source for downloaded tiles. Applications which frequently alternate between a limited
  number of map model configurations may want to consider using a different cache for each.
  
  @since 0.5.1