code: private void executeDelKeySpace(Tree statement)
              throws TException, InvalidRequestException, NotFoundException, SchemaDisagreementException
      {
          if (!CliMain.isConnected())
              return;
  
          String keyspaceName = CliCompiler.getKeySpace(statement, thriftClient.describe_keyspaces());
          String version = thriftClient.system_drop_keyspace(keyspaceName);
          sessionState.out.println(version);
  
          if (keyspaceName.equals(keySpace)) //we just deleted the keyspace we were authenticated too
              keySpace = null;
      }
docs: Delete a keyspace
  @param statement - a token tree representing current statement
  @throws TException - exception
  @throws InvalidRequestException - exception
  @throws NotFoundException - exception
  @throws SchemaDisagreementException