code: public static S3Versions forKey(AmazonS3 s3, String bucketName, String key) {
          S3Versions versions = new S3Versions(s3, bucketName);
          versions.key = key;
          return versions;
      }
docs: Constructs an iterable that covers the versions of a single Amazon S3
  object.
  
  @param s3
  The Amazon S3 client.
  @param bucketName
  The bucket name.
  @param key
  The key.
  @return An iterator for object version summaries.