code: public BatchMutation<K> addCounterInsertion(K key, List<String> columnFamilies, CounterColumn counterColumn) {
      Mutation mutation = new Mutation();
      mutation.setColumn_or_supercolumn(new ColumnOrSuperColumn().setCounter_column(counterColumn));
      addMutation(key, columnFamilies, mutation);
      return this;
    }
docs: Add a ColumnCounter insertion (or update)