code: private void executeDelColumnFamily(Tree statement)
              throws TException, InvalidRequestException, NotFoundException, SchemaDisagreementException
      {
          if (!CliMain.isConnected() || !hasKeySpace())
              return;
  
          String cfName = CliCompiler.getColumnFamily(statement, currentCfDefs());
          String mySchemaVersion = thriftClient.system_drop_column_family(cfName);
          sessionState.out.println(mySchemaVersion);
      }
docs: Delete a column family
  @param statement - a token tree representing current statement
  @throws TException - exception
  @throws InvalidRequestException - exception
  @throws NotFoundException - exception
  @throws SchemaDisagreementException