code: public Bucket enableDefaultEventBasedHold(String bucketName) throws StorageException {
      // [START storage_enable_default_event_based_hold]
      // Instantiate a Google Cloud Storage client
      Storage storage = StorageOptions.getDefaultInstance().getService();
  
      // The name of a bucket, e.g. "my-bucket"
      // String bucketName = "my-bucket";
  
      Bucket bucket =
          storage.update(BucketInfo.newBuilder(bucketName).setDefaultEventBasedHold(true).build());
  
      System.out.println("Default event-based hold was enabled for " + bucketName);
      // [END storage_enable_default_event_based_hold]
      return bucket;
    }
docs: Example of how to enable default event-based hold for a bucket