docs: public void listInstances() {
      System.out.println("\nListing Instances");
      // [START bigtable_list_instances]
      try {
        List<Instance> instances = adminClient.listInstances();
        for (Instance instance : instances) {
          System.out.println(instance.getId());
        }
      } catch (PartialListInstancesException e) {
        System.err.println("Failed to list instances: " + e.getMessage());
        System.err.println("The following zones are unavailable: " + e.getUnavailableZones());
        System.err.println("But the following instances are reachable: " + e.getInstances());
      }
      // [END bigtable_list_instances]
    }