code: @Override
      public final boolean contains(Object o) {
          @SuppressWarnings("unchecked")
          final K key = this.getElementKey((T) o);
          final Queue<T> queue = this.keyedQueues.get(key);
          if (queue == null) {
              return false;
          }
  
          return queue.contains(o);
      }
docs: /* (non-Javadoc)
  @see java.util.concurrent.BlockingQueue#contains(java.lang.Object)