code: public void readWriteTransaction(final long singerId) {
      // [START readWriteTransaction]
      TransactionRunner runner = dbClient.readWriteTransaction();
      runner.run(
          new TransactionCallable<Void>() {
  
            @Override
            public Void run(TransactionContext transaction) throws Exception {
              String column = "FirstName";
              Struct row =
                  transaction.readRow("Singers", Key.of(singerId), Collections.singleton(column));
              String name = row.getString(column);
              transaction.buffer(
                  Mutation.newUpdateBuilder("Singers").set(column).to(name.toUpperCase()).build());
              return null;
            }
          });
      // [END readWriteTransaction]
    }
docs: [VARIABLE my_singer_id]